I think Singapore is fab for kids. Quite a lot to do and you don't have to drag them from mall to mall.
The Chinatown in Singapore has a couple of streets, a little like Petaling Street in KL so good for a wander (late afternoon when it's not as warm) and quite a few of them sell children's cheongsams.
There is a shop in Chinatown called Yue Hwa (think I've spelt it right) which has everything chinese over about 4 or 5 floors and they will have traditional chinesewear for men, women and kids. They tend to stock better quality stuff than you would find in the street market.
For the kids, we find a day in Sentosa pretty good fun, you can choose to do attractions or just sit on beach, grab a few drinks and let the kids play.
There's also the Zoo / night safari or a water theme park called Wet Wet Wild.
or there's the Singapore Ducktours or a boat ride along the river.
For something a bit more local, head over to the East Coast park, hire a couple of bikes with child seats and go cycling, you can choose to have breakfast there and then go cycling or go cycling before stopping for dinner.
Are you visiting family in KL or holidaying?