The Rusty Parrot was neat if the kids are in to pirates. We took our boys a couple of years ago when it first opened - they were 6 and 3 then.
https://www.tripadvisor.com/Attract...ce-Philipsburg_Sint_Maarten_St_Mart.html

There’s a gelato place on the “boardwalk” in Philipsburg and they have a decent playground on the beach with swings and slides that’s free to use.
https://www.tripadvisor.com/Restaur...g_Sint_Maarten_St_Martin_St_Maarten.html