Kids can be very strong players. You should never feel humiliated to play against an equal opponent. Just go and enjoy the atmosphere, many masters have been beaten by kids before, it's not something to sweat over.
What to expect in an OTB tournament
I remember my first OTB tournament and the biggest difficulty I had was dealing with the clock AND remembering to write the moves down .......
That whole "writing the moves down" thing is really difficult the first time or two.
It's probably to late for the OP to read it, but I would strongly encourage anyone going to their first OTB tournament to play against a computer, and write down the moves as they go, for practice. Or take a scoresheet to their local chess club if they can.

r ewriting the moves down: I used to be a bit nervous about this too before my 1st OTB tournament game, but I practiced playing against Fritz using the 3D board which doesn't feature coordinates - so it was very easy on the tournament board with coordinates after that. The only issue is if you forget to denote a non-unique move (Nbd2, R1d1, ...) - at my tournament it doesn't matter because the scoresheets are not turned in, I don't know what they do about wrong or missing notations at tournaments where the scoresheets are turned in ...
You should leave the board (toilet break etc.) only after you have made your move and it's your opponent's move. The first reason for this is that so you do it at least partially on your opponent's time, and the second reason is that otherwise it could be suspected that you are going to phone some chess master you know for help ... If you come back, your opponent has already moved and you're not sure what the move was, you can look at his scoresheet or just ask him, that's no problem.
I've been practicing keeping my own score even when playing computer games. It can be tricky, especially on the moves like Nbd2, but I think I should be fine. I used to do it for fun as a little kid, too, but it'd been awhile. My board does have the ranks and files marked, but opponents' boards may not.
Does the tournament provide scoresheets or do I need to bring my own?

You're going to a big tournament so the tourney should provide scoresheets but I suggest you also bring your own (like buy one of those 50 game pad things or whatever)
And also you should bring your own board (and your own clock if you have one but its your first time so don't worry about it if you don't have one) there and I'm assuming the tournament doesn't provide boards but if your opponent's board doesn't have coordinates just use your own.
And btw, make sure you know the rules for claiming draws/when you dont have to notate.... etc.
This LIKELY WON'T HAPPEN but the earlier you know it the better lol. So basically, I was at a small tourney where I got into major time trouble <1 min with a 5 sec delay and I had a K+N vs. opps K+R which is pretty much a draw. HOWEVER, I wasn't notating (b/c it was <5min on my clock) and so when the clock counter reached 50 moves after when the situation arose, I tried to claim a draw but I couldn't (and then my mind literally heated up and I blundered later...) bc I didn't know you had to inform the TD first so make sure if this type of situation comes up you inform the TD immeadietly. Same thing applies for 3-move rep claims if you aren't notating due to time pressure.
And I also suggest you use a 5 s delay for all your games. If your opponent doesn't want to you can force them by telling the TD.
Tomorrow's the big day! The tournament has already begun (I'm playing the two-day option that doesn't start until tomorrow), but I see myself on their web site. I kinda wish I hadn't registered with the USCF with my full name. It looks odd written out like that.
I appear to be the only debutante in the tournament. Shame there's no unrated prize.
I also can't help but notice there are an odd number of players in the two-day pool, and being unrated puts me at the bottom, so I wonder if I'm doomed to a first-round bye. I'll e-mail the tournament tonight and ask. Might be nice to sleep in in the morning.
Got a quick response. Unrated players normally are not byed, and they expect entries and re-entries up until the deadline tomorrow, so it's too early to assume anyway.
I don't want to turn this into a running thread just for my results, but I'll say that I have started the tournament and sit at 0.5/2. I'm having a fantastic time, even though I've got a long lunch break because I completely botched the opening of my second game with a very rookie mistake and lost very quickly.
The first game was pretty hard-fought and I didn't make any blunders. Fell down a pawn early, but felt like I had a solid position and eventually ended up in an end game with three opposing pawns and a knight on both sides. The kings were in opposition in the middle of the board, but my knight was in better position and his had been driven to the edge, and he was down to 1 minute on his clock vs. 17 for me. I don't have access to computer analysis right now, but I'm about 80% sure it was dead drawn, with maybe a 20% chance I had some play for a win. He offered a draw and I probably should have declined it. I thought maybe I had some vague winning chances and could have run him of time. But I figured it was probably a draw anyway, and it didn't feel sporting to try to run him out in a position like that, and I really, really wanted to make sure I didn't go 0-fer the tourney, so I accepted.
I'll post my games in the analysis/showcase boards tomorrow, as the case may be.
There are 8 people in the U1400 2-day pool (it will merge into the larger pool after the third round this afternoon), and I think there are 2 teenagers and the rest are adults of varying ages. So that makes me feel better. Everyone has been very nice, too.
U1400
Overall: $1,000-$500-$$300
U1200: $250-$150
U1000: $225-$125
As unrated, I'm only eligible for winning back my $100 entry fee unless I play in the open section, which obviously wasn't a good idea. I don't think I was ever a threat to win any money, though.
Okay, some experiences.
First, I'm sitting at 1.5/4. I won't be posting any games, because apparently while I thought I was taking accurate notations, what I wrote down only vaguely resembles what happened on the board. Trying to recreate the games with the accurate moves has been problematic...
Game 1: Tough draw. Fell behind a pawn early, battled to an even position, accepted a draw in a position where I *maybe* had a win but probably not, just happy to get the draw.
Game 2: Blundered opening thoroughly and resigned 18 moves and 5 minutes in, probably could have resigned comfortably after about 8 moves.
Game 3: Wild game that had both sides castling kingside only to have that side blown open with dueling attacks, then it simplified down to her R+R versus my R+N, defended awhile, she let me fork the rooks, I thought I had the draw, but she outmaneuver my king in the endgame and won the pawn race.
Game 4: Tough game, made a slight inaccuracy and it cost me two pawns, was down three pawns and nearing the endgame and cursing the world and how the standard of play was *much* higher than I would have guessed and was to be honest a little discouraged. I was playing my best, but my fellow U1400ers were much better than I expected. Don't they ever make any mistakes that can be capitalized on? And then she suddenly walked her queen into a skewer and I scraped an undeserved win.
The whole experience has been amazing, I wholeheartedly recommend it to anyone and everyone who plays chess. There are a few children, but they are a large minority and I would probably enjoy playing one. Oddly enough, my last two rounds have been against women, when I'd guess only about 5% of the tournament is female (if I may be a little piggish, the fourth-round opponent was drop-dead gorgeous).
The tournament staff is helpful, and this being a large (expensive) tournament, everything is provided. They did ask if anyone had chess clocks because they were running low, but they have nice boards, scoresheets and nifty little scoresheets.
A tournament game, while friendly, is *intense*. I see what people mean about OTB being the best way to play. When I'm playing on the computer, if I blunder away a game, no big deal because I can fire up a new one. But here, there's this tangible feeling that every move, every piece really matters. There's a difference between playing online, even in a slow game, when you can check our e-mail and tab around, against sitting over a board and really focusing on a game for several hours.
I'm proud of the fact that in 3/4 games, mine was one of the last going on in the section. Taking my time is key (I wish my opponents would hurry a little more and play a little less well, though :) ).
There are about a dozen grandmasters there, and the top boards are in a little roped off area that you can walk up to and observe, with display boards up on a stage above them. It's funny to see that the grandmasters are a diverse bunch: young and old, men and women, well-dressed and sloppy. You'd never know seeing them walking down the street that they are among the best in the world. Watched Nigel Short play for awhile when I had a break, tried to guess his moves before he made them. Went four for five on that! (It wasn't a complicated position...)

Thanks everyone so much for the answers. I really am excited about this and will of course post my experiences.
On the kids thing, it's not that I'm worried about playing strength. There are probably a lot of kids out there much better than me. I'd just feel a little awkward if I'm at a board with a 9-year-old and there is nothing but 9-11 year olds at all the boards around me as well. But it doesn't seem like that'd be the case. I'll just try not to think about it if it is.
On resignation, I generally don't it. If I'm in a lost position, I'll generally just speed up to blitz speed so as not to waste my opponent's time, but I want to always play it out.
On results, I'll be ecstatic with 0.5/6 at U1400. I don't want to get completely skunked, but anything else is fine.
I'm playing the U1400 section (I'm currently rated ~770 in the USCF but I've only played 4 rated games) at the National Chess Congress in Philly this weekend. My first round I got a 1 point bye due to an odd number of players. My next game later that day I was crushed by an 8 year old kid with his father standing behind him with an open laptop (which made me feel like he might be cheating when the kid would leave the room with his father). This morning, my opponent (7 year old girl) showed up with 15 minutes off of her clock and puked. She went to the bathroom and I went outside for a couple cigarettes. Shortly after I returned, she did as well. We were pretty evenly matched but she ended up beating me on a blunder. My second game today, I was matched with a 35-40 year old male, and I was certainly happy to be playing someone over the age of 10. He was rated 1375+, and I ended up crushing him. At the end, he outstretched his hand. I said "You resign?" just to make sure he wasn't trying to swindle me into a draw and he said "Yes". I hope that this will be the biggest upset of the tournament (not sure if there is a trophy or not). I have two games tomorrow and if I can get 1 point out of it to finish 3.0/6 I will be thrilled. Here is my most recent game: Time controls 40/2 SD1

Sounds like an interesting experience, even though I can't play. Just be glad you didn't play in the over 1400, like you were talking about before.
Thought of another question: Is there a formal procedure for capturing, i.e. what order you touch the pieces and such? I usually just slide the captured piece off the square with my piece, then remove it from the board.
No. If you touch your opponent's piece with your hand or with another piece, you must capture it. If you touch one of your pieces, you must move it. The order is not important.
If there are no legal moves that you can make under those conditions, there is no penalty for touching your own piece or your opponent's piece. e.g. if you are in check, and you touch a pawn that cannot be moved in such a way as to get you out of check, there is no penalty for touching the pawn.
In USCF rules, there also isn't any requirement to touch the king first when castling, but it's a darned good idea to do so. It will save a lot of grief because that is commonly believed to be the rule, even by some TDs, and it is the rule for FIDE.
When promoting a pawn, there is no rule about the order in which things have to happen. Also, if you touch an opponent's off board piece, you aren't required to promote to that piece until you release it. e.g. you move a pawn to the back rank. You remove the pawn and grab a queen, and place it on the board. Without letting go, you realize that a queen would create a stalemate. You can pick up the queen, and grab a rook instead, as long as you didn't take your hand off of the queen when it was in the promotion square.
The whole thing about shaking hands is also a bit of a myth. The key is that as soon as you resign or accept a draw, you can't take it back. If you shake hands as a signal of resignation, you're done. If someone says "draw?" and offers a hand, and you shake it, it's a draw. If someone extends a hand wordlessly, and you shake it, it means nothing at all.
I find it embarassing and offensive that an IM would encourage children to cheat with trick handshake offers, as described in an earlier post.