Tumbles in Williamstown is great. Was just there today with feeb.
Play Hut in Altona (part of the Westgate indoor sports centre). This one you take your own food and drinks. It's for kids under 6yrs old only. It was a favourite with my kids.
Monkey Mania in Footscray is also supposed to be great.

Tumbles is great!!

Kidzmania in west footscray

Monkey mania Docklands

Kidz play shak Altona is good too