Not sure when he's going, but we came back on Tuesday this week, and Abercrombie and Hollister were doing 40-50% off everything in store. The problem for you is going to be sizing issues, presumably?
Normal price, Gap is pretty much consistent with us here, but you can get some great bargains in their sales and outlets.
Old Navy is great for kids, and I get my PJs from there.
J Crew is still quite expensive (nothing like the pricing here though), but if he's going to an outlet, J Crew Factory is worth a look at (but note that the stock is different from a normal J Crew). I like Crew Cuts for the kids too. TBH, though, Gap, BR, RL, Hilfiger and J Crew are pretty similar - it's your archetypal US fashion, and every other store carries it.
I like Victoria's Secret for underwear (I buy their 5 for $26 pants and their body bras), but it's not particularly cheap. They often do a deal where if you buy something, they give you a discount at the bottom of your receipt, so worth going twice.
Crocs are cheaper, especially at outlets, good for the kids.
I usually buy RL polo tops for my son in the outlets - great quality and decent pricing.
DKNY for a cozy or 2 (again super cheap in the outlet - $49).
I've been wearing Lucky Brand jeans now for quite a few years, so usually stock up when visiting.
Non-clothes: MAC make-up, Secret deodorant in delicious scents, I love the Hollister body scents for women, Almond and peanut butter M&Ms, Skylanders for the kids (ToysRUs often has a deal), Lego. Dollar is weak at the moment, so loads of bargains to be had.