The Royal Lifeguard Dog Ultimate Swim Diaper seems to be very comfortable for my little Toddler.  He has no argument wearing them during swimming lessons under his board shorts while he refuses to wear swim trunks with mesh liners. Although he has not had an accident in them, I've noticed when removing them that water had pooled inside.  This leads me to believe that, should he have an accident, things would be contained.  Regardless of how well they work, please check your child's diaper on a regular basis.  Nothing can contain messes 100%!