Le Meriden in Cyberport would be a good choice if it was near where you live, or they didn't mind a 15 min taxi ride into town/thru the western tunnel to Kowloon.
It has the grass area adjoining, a nice pool and a child friendly restaurant (plus a little bar area that is good to use during the day for little ones to run around as it doesn't open until the late afternoon. Handy for Ocean Park also.