I'm so happy your son is going into band!! It's going to make scholorship searches much more easier once he's old enough for college!
I'm kinda leaning towards trumpet...I mean..my music scholorship is for it..lol
But I will say being a low brass is -very- fun, especially when playing some of those throaty-deep-seat-shaking songs!! But, have you looked at maybe clarinet? I started out on it (5th to 7th grade) then went to bassoon (7th grade to college) and played trumpet for marching (9-college). The colleges absolutely LOVE those 'odd' instruments like the bassoon, baritone sax, baritones, and will give out very nice monies for experience in those!! So when he gets up to middle school let him switch to a larger instrument!! It'll break the boring-ness of the starter horn phase and give you the chance to have less money to pay out for his college!!
....and one more thing..don't let him quit!!!
