Where are you staying - maybe people who've stayed there can let you know about facilities at your
hotel or close by. There's at least one playground - probably more but as I don't have little ones I don't notice these kinds of things. There's a water park in
Marmaris - my son went there - £8 for 2 horus or £10 for the day (seems strange) - can anyone else give prices?
the majority of bars/restaurants have music, dancing - loads of choice. Some of it can be more adult so hopefully that will go over your little ones heads - I don't mean excessive here. Not knowing the ages it's difficult to suggest anywhere. You might find boat trips too long a day if they're young, you could though take them on the water taxi to Marmaris - about 30-40 mins. Other boat trips are all day long and tend to be swimming at every stop - ie the only way you get off the boat is jumping in the sea but you probably did that on your previous visits.
Hope someone else can give more info.