Hi... you might find this article informative https://sg.theasianparent.com/10-unique-singapore-birthday-venues-for-a-kids-party
Try HDB public spaces... like areas where some hold malay weddings, funeral services etc
Depending on your budget and number of pax..Can try hotel or restaurant?
Maybe you can try Kith cafe at marina sq or any kids friendly cafe...
Chalet would be good. House have to clean up after that.
Relative's condominium function room?
Can consider Little house of dreams?
Bove/ hotel/ orchid country club?
You can try Bove, country clubs?
Hotels, and recreation centres?