Hard Rock Hotel, it has a nice swimming pool and kids club for kids 3 years old and above. Share with you a link of list. Hope this helps. https://sg.theasianparent.com/kid-friendly-staycation-spots-in-singapore/
Shangri-La’s Rasa Sentosa -shallow pool & there’s a tree house with entertainment for younger kids
Hey! Hope this article is useful: https://sg.theasianparent.com/family-friendly-hotels-in-singapore
thanks