Are there any fountains in Paris that are currently open which children can actually play in ?
Children play in the fountain at the Parc André Citroën, which is one of those where the water squirts out of the pavement.
There is a sort of waterfall fountain in the park behind Sace Couer that I have seen kids play not in but with -- they put balls in the water above and watch them go over and below and then fetch them and do it again.
Oh yes, I forgot about République. It is not exactly a fountain but a wet rectangle of pavement in front of the café in the square. Children love to slip and slide all over it.
I even made a little video showing it on inauguration day last year: https://www.youtube.com/watch?v=sIB-YeWpa54
What about the fountains at Pompidou? I think I remember kids playing in them? or am I making stuff up again? In any case, that's a fun area for kids.
Wading or playing in the Pompidou Stravinsky fountain is strictly verboten. Absolutely not on the list of play fountains.
When the temperature rises above 35°, you will see all sorts of forbidden fountain play around Paris, but that is probably unlikely for the rest of the year even if tomorrow is supposed to be "hot" (27°).
The Republique "water mirror" is activated in the summer.
The fountains on boulevard Richard Lenoir have usually been on when the open-air market is in swing - Thurs and Sun mornings - can't swear to any other times or days, since that seems to be intermittent.
Anybody know about the fountains and pools around the pyramids at the Louvre? Probably not possible, but it's a thought...
There are signs telling people in the Louvre courtyard that it is forbidden, which is proof positive that people do it.