This is probably a really stupid question, but...
What is a baby girl (or boy, I suppose) supposed to wear under her dress? Obviously she has a nappy on, but should she have anything on over the nappy? Some shops sell matching pants with dresses, so no problem there. But what if she has a dress without matching pants? When the weather is cool, then tights, leggings or a vest/body suit are probably sensible, but what about when it's hot? I've never seen a shop selling plain pants for babies.
I think I am perhaps thinking too hard about this!