You wouldn't sue yourself as the parent/guardian of the child - you look around for someone, anyone to blame.

When I took a 5yo to a pool which had multiple lifeguards I put her in a lifejacket and stayed within arm's reach of her. Playing in a pool is great fun but it is very high stakes. No way I am going to leave a child in such a dangerous situation and hope it works out. Making sure your child survives a trip to a pool is your responsibility.