What size underwear for 3 1/2 yo boy?

ss+el · February 2012

DS is finally agreeing to wear underwear, but I bought his a year ago, so it's size 2T. (Thomas from the baby aisles at Target). It's fitting fine for now, but there's no way it'll fit after his next growth spurt. He also needs more anyway, went through all but 1 pair yesterday. Should I go for the 3T/4T combo size from the baby aisles at Target (he wants Sesame St.) or jump over to the smallest from the boys' dept? Do they fit differently?

FWIW, he is squarely in size 3T clothes, still fits in his 2T Circo jeans. He tends to be just slightly tall & skinny. (34lbs, 39(?)")