I bought this for my son who was almost 3.  The 3t/4t Fit him very well and he's about average weight and just a little taller than an average 3yr old.  He also wears Carters 3T shirts/pants and the pants are just now the right size w/o shoes.

The outfit works and was durable enough to last a couple halloween parties without problem.  The hat is ok although I got him a racing helmet that he preferred to wear.  Because he's 3.  And racing helmets are awesome.

The flag, book, and cars that came with the outfit are basically throw-away items you'd get at a dollar store.