V.T.
It probably isn't worth it to the companies to make them smaller, at least the disposible kind. Kids aren't suppose to wear sunscreen until 6 months, so they probably assume, a majority of younger kids aren't going to be in the pool, since most pools are outdoors. That being said, I used Pampers on my daughter since they seem to run smaller than the size on the package. They do make reusable swim diapers. I just bought a reusable ones by iPlay for my boys. I just googled their website and they have some that go down to 3 months.