The biggest and best are Banksia Park and Birrarrung Park
Personally, I have enjoyed going to Bulleen Park on numerous occasions for family picnics, walks etc. Here is a little bit of information regarding Bulleen Park from the local council website:
Bulleen Park provides important community facilities including sporting ovals, an aeromodellers field, archery field and playground. It also accommodates some informal recreational open space along the Yarra River, particularly for walking and bike riding.
Facilities and Points of Interest:
Yarra River recreation trail
Sports ovals for football, cricket, soccer
Yarraleen Cricket Club
Bulleen Templestowe District Junior Football Club
Yarra Junior Football League
Yarra Bowmen Archery Club
Doncaster Aeromodellers Club
Toilets (near archery and aeromodellers field)
Off street carpark
I was amazed by how much greenery is in the area. It really is an ideal place for active kids and people who love the outdoors.