My little is 17 months old and she normally wears size 12-18 months and some brands 9-12 months. So I bought size XL and it fits perfectly. She had her first swimming class and she was cozy inside her swim suit. Plus, the colours are really nice!
Bought the xlarge for my granddaughter who is 15months with hubby legs. I was so pleased with the all in one easy to get on and a perfect fit. Struggled a bit to get off, perhaps the zip at the back could be a little longer. Always a struggle getting wet clothes off though. I can recommend this product.