In my opinion I think they should at least be 6 months. But idk that's when I took my kids in the pool or older
I've seen people being little newborns like a month old into pools the earlier the better it's good to get them used to it early but indoor would be best cause their not really supposed to be in the sun much till 1 year old
As long as they have there first shots I plan on taking my little one in at 3 months
I'd say probably about 8 months