I think the best ones are Boots ones, which are flat ones which you velcro and then tie. DO NOT get a pull up swim nappy. Because, if they poo (which will probably happen), the water gets in with the poo, swirls it all around, some poo escapes (because you can't control the tightness round legs/waist) and THEN you have to pull the whole lot DOWN. Over their KNEES. And the wet, pooey, gloopy mess goes all over their legs, their knees, the towel, you. Oh yes, I speak from experience.