I have age 5 1/2, 3, and 19 months. The 5 1/2 year old is close to swimming, *I* could probably get him going, not at all scared to jump in, put his face in, etc.
3 year old pretty much plays in the water.
Baby LOVES LOVES LOVES LOVES LOVES to swim and crawls around when he can with his hands touching bottom and feet up behind him because he is imitating big swimming kids.

(My first to be born in water and definently my biggest fan of pools this young.)
However....I do not trust the older 2 judgement fully on where they can/can't be. And the baby needs 100% supervision as he will still very occasionally fall while walking in the water.
AND I am pregnant. So we have to be somewhere where I can jump out easily and follow the youngest if I need to.
That all taken into consideration, the only places I am willing to take all 3 of them is the small, not at all busy kiddie pool that is about 14 inches deep with a tiny little slide for baby to play on, or the spray park. There is one other pool in town that is a kiddie pool with a 1 foot some inches side and a 2-2.5 foot side, but even there, it's harder for me to jump out and follow if baby decides he wants to play on the bridge that goes from one side to the other.
The older two though love it and can handle both sides just fine. It's baby DS I worry about and I really don't put it past him to just jump in.
There are 3 other pools in town that are 0-entry going to almost too deep for DD before the rope--and one without a rope at all that goes up to 3 foot. I will only go to those with the big kids while the baby is napping at home with my mom. Period. There is just no way I can keep an eye on all 3 to the point that i need to in the water.
And I do not put any sort of floatie device on them. (arm things, life jacket. etc) Either they are comfortable and can touch or they don't go in. I know at least one pool here does not allow life jackets and floatie things.
Last year when DS2 was a baby I kind of lucked out in that DD didn't like any of the little pools, she said the water was too cold and would not go in. So she was the one who napped, we only took her to the spray park.
The two years before that (DD as under 6 month infant and as 18 months-ish toddler), we only went to little kiddie pools or the spray park, so I felt totally comfortable with the older one's ability to handle it without me right at his side. (he was age 30-some months that first summer and 3.5 the second.)
Oh also all the pools we go to have lifeguards, so on the off chance something happens....AND they are not reading, the ones I see, they are actively standing, watching, correcting children who are hanging on ropes, not waiting for people to move out of the way of the little slides, etc. etc. So on the off chance something happens while I'm attending to one of the others, they will most likely be noticed!
I took the 5 year old and the baby to one of your typical 'big pools' last week, it is NOT an experience I will repeat. The baby did not enjoy the floatie for very long, the 5 year old could only touch in a little bit of the pool, and afterward he voted that the places we go with just him and sister are *way* better.