Holiday in melbourne

I don't have kids but I am a regular user of TripAdvisor.com
it's an excellent site with great info and you can specifically Google things like travel tips for kids, top 10 things to see, or top 10 things to avoid etc.

All I can think of is IMAX but you don't say how old your children are.

Hope you have a good holiday

hey!!
    i am from pakistan and after 3 years i will come Australia  for study so,please tell some some information about the universities and courses and all other things............

The Melbourne Aquarium is quite impressive, and lots of fun. I would actually recommend ACMI- Australian Centre for the Moving Image- which is just next to Federation Square. They have a kids corner with lots of planned activities, mainly around cartoons, animation, video games etc. The National Gallery (Ian Potter Centre) is next door and also has a big kids corner.
Depending how old your children are, both the Zoo in the city (Parkville) and the Werribee Open Safari are worth a look. The Werribee Safari in particular is really quite spectacular.
Hope you have a good time!