There is No.Good.Reason for me to buy DS a Valentine's onesie. None. I don't even like Valentine's Day! (DH and I have never "recognized it.") But don't kids just make everything more fun??!!!
I mean, sure, once he's in school and they have class "parties" or whatever, that might make sense. But now (when he'll just be in daycare all day)? It's just for my amusement (As were his Christmas outfits. And as will be the birthday outfit I'm already searching for!)