A burning house is not "a pool".
In my country you can't watch a kid drowning in a pool* but you are not obligated to help anyone in a burning house, since that would put you in danger too. I assume it is the same ~everywhere in the world, including the US.
* assume rescuing would be fairly safe, you are a good swimmer, you have lifeguard education, the weather is nice and the kid is small. AFAIK rescuing drowning people is dangerous as they can pull you down.
A drowning child is of fairly limited threat to an even halfway competent adult swimmer. Even at maximum panic/flailing, they just don't have the mass or strength to prevent you from at least treading water.
I'm a good swimmer, and 50 pounds of thrashing, scratching and climbing feels dangerous.