K, so the first longies were in size 18-24, and they were too big, but with a drawstring waist, and a big cloth diaper, they'll stay up. Then I made a pair of 12-18 sized shorties, equally too big. So here's pair #3, sized 6-12 month, over a cloth diaper, and they fit my 22month old PERFECTLY. I'm sooooo pleased with the finished product!