rating for tournaments

From what I am reading here, are you saying that someone that has never played in a tournament can come in as unrated and join USCF on the same day and play in the higher ranks such as class A or B and never have to work their way through the lower ranks at all.  Is this why the opening tricks sometimes work against the Masters?  I know this family has won a few games against these players by using the opening maneuvers.

And I have another question.  I have a child that tried chess but did not do well when they were under 10. It's been a few years.  He has studied and is now beating the older siblings, yet his rating with USCF is under 400.  In our chess club, he is one of the best players.  Since the older ones are bring home checks from tournaments, he now wants to play in the tournaments.  Is it fair to the other players for him to come in rated at below 400 when he's really playing at over 1400?  How does USCF handle this?