U could choose Najdorf as the most popular Sicilian variation.
Learning the Sicilian defense, your advice please

If sicilian isn't the right defense for 1. e4 in your opinion; what would you suggest? I'm very open to suggestions as I think I'm stuck currently.
I should probably mention why I'm looking into the Sicilian Defense. One part is that I want something for 1. e4. Another reason is that it is an aggressive defense. I don't personally like very aggressive chess games because my tactics isn't good, but my son is very good at tactics so I thought this open might be good for him.

I've not looked at the Najdorf. The only variant that I've looked at is the Open Sicilian. The book (Chess Openings for kids) I have contiunes with Closed Sicilian and Grand Prix attack and Alapin sicilian.
I'm hoping to just study one of its variants and use it in every game. I'll take a look at the Najdorf.

I'm hoping to just study one of its variants and use it in every game.
The problem with that is that there are a number of anti-Sicilians that White can use to keep you from getting to the variant you want to play. A partial list would include the Alapin, the Rossolimo, the Closed Sicilian, the Grand Prix Attack, the King's Indian Attack, the Smith-Morra Gambit, and the Wing Gambit. Thus, you could put in a lot of time and effort to learn how to play the Najdorf, for example, and rarely get a chance to play it.
If you settle on the Sicilian, DeirdreSkye correctly states that you should initially focus on the Scheveningen structure as it appears in a number of variants. It could in fact be thought of as the basic Open Sicilian structure. A good starting point for learning how to play the structure is Soltis's "Pawn Structure Chess", which has a decent basic explanation of it.
If you want to look at alternatives, I would suggest either 1...e5 or 1...e6 as a response to 1. e4. The openings resulting from 1...e5 generally produce classical chess structures, while 1...e6 is of course the French Defense. Both moves can produce rich play from which you can learn a great deal.
Around 2010, IM John Watson wrote, "... For players with very limited experience, ... the Sicilian Defence ... normally leaves you with little room to manoeuvre and is best left until your positional skills develop. ... I'm still not excited about my students playing the Sicilian Defence at [the stage where they have a moderate level of experience and some opening competence], because it almost always means playing with less space and development, and in some cases with exotic and not particularly instructive pawn-structures. ... if you're taking the Sicilian up at [say, 1700 Elo and above], you should put in a lot of serious study time, as well as commit to playing it for a few years. ..."
Possibilities:
Starting Out: Open Games
https://web.archive.org/web/20140626232452/http://www.chesscafe.com/text/hansen134.pdf
Starting Out: Ruy Lopez
https://web.archive.org/web/20140627024240/http://www.chesscafe.com/text/hansen53.pdf
First Steps: 1 e4 e5
https://www.newinchess.com/media/wysiwyg/product_pdf/7790.pdf
The Petroff: Move by Move
https://www.newinchess.com/media/wysiwyg/product_pdf/7530.pdf
Starting Out: The Sicilian
https://web.archive.org/web/20140627122350/http://www.chesscafe.com/text/hansen123.pdf
First Steps: The French
https://www.newinchess.com/media/wysiwyg/product_pdf/7611.pdf
Opening Repertoire: ...c6.
https://www.newinchess.com/media/wysiwyg/product_pdf/7673.pdf
The Pirc: Move by Move
https://www.newinchess.com/media/wysiwyg/product_pdf/7604.pdf
First Steps: The Modern
https://www.newinchess.com/media/wysiwyg/product_pdf/7700.pdf
The Scandinavian: Move by Move
https://web.archive.org/web/20140626232217/http://www.chesscafe.com/text/hansen171.pdf
https://www.newinchess.com/media/wysiwyg/product_pdf/7270.pdf
My First Chess Opening Repertoire for Black
https://www.newinchess.com/media/wysiwyg/product_pdf/9050.pdf
The Alekhine Defence: Move by Move
https://www.everymanchess.com/downloadable/download/sample/sample_id/69/

Don't start with the Najdorf. Too complex. My suggestion would be that you spend some time playing against the sicilian with the white pieces to give you a feel for what black can and maybe can't do. You'll feel a bit more confident when you do those things yourself or you will, at least, learn what you should have done with white.
The scandinavian is a very simple opening. White almost always responds the same way with slightly different move order. I don't have very much experience with the sicilian though.

If u want something solid, the best sicilian in my opinion is accelerated dragon.
Simple to learn and easy to play.
Najdorf, Scheveninguen, Paulsen, Svechnikov, etc... Forget about it, u will suffer many painful defeats without learning anything (or let's say learning to lose).
Personnally, I don't like to advocate sicilian : 1...e5, 1...e6, 1...d5 are more easy to handle and more instructive.

When I was new I picked the Sicilian because that's what Kasparov played, so that means it's good right?
But then I switched to ...e5 and enjoyed it much more.
Don't pick an opening because of move 1. Play over top level games and pick an opening because you like what you see on move 10, 15, 20 i.e. the middlegame.
For example the recent Tata Steel tournament (picking a historical match or tournament is fine too).
http://www.chessgames.com/perl/chess.pl?tid=92172
Just click through the games quickly. 15 minutes a day and you'll have played through the whole tournament in 1 week. Just to get a feeling for what kinds of middlegames are out there. If you see something you like, pick that opening.
My 2 cents.
"... A typical way of choosing an opening repertoire is to copy the openings used by a player one admires. ... However, what is good at world-championship level is not always the best choice at lower levels of play, and it is often a good idea to choose a 'model' who is nearer your own playing strength. ..." - FM Steve Giddins (2008)
I have no real strategy when it comes to 1. e4, and that means I usually waste a lot of time in the open. So, I'm thinking about learning the Siciian defense, and , as you know, there are many variations.
Do I just pick 1 variation and learn it? Or are all the Sicilians related enough such that I should be familiar with all those variations?
Or is there another defense that is easier? Like the London system for white (I don't play it, just an example). I'd like something solid to reply 1. e4.