Gerber Baby Girls' Waterproof Pants

What size for a 20lbs 4mo who has chunky legs? Want the to last a bit just cover his cloth diapers.

Will these work to put over diaper to stop nightly leaking for 6 month old? I've tried every diaper, different sizes but yet she is wet every morning.

Can these be worn in the pool?

My daughter weighs 50lbs at 3 years old. She is currently in a six 6 diaper and panties. What size in these would work for her?