Have you checked out the 2011 Children's Season held at various museums? We have been to quite a number of them so far, and still plan to go to the rest :-)
Organised by the National Heritage Board and Museum Roundtable, 2011 Children’s Season will be held from 14 May to 31 July 2011.
My kids have a ball of a time there; I believe yours will too. My kids learn so much about so many things and have fun at the same time.
If you can, go over during the weekdays, since it can be very crowded during the weekends (depending on where and what time you go). However, many activities for kids are usually planned during the weekends. Most of the activities are free, but we have to pay a small token for the rest. So, do check out the website before you go.
Have fun and see you there!