More stuff to do in Singapore:
The Singapore Flyer is a fun half day out. It has gardens at its base and views over the F1 track plus all of Singapore.
A cinema trip in Gold Class (at the Great World City or Vivocity cinema) is a great experience for kids (think huge armchairs that recline, blankets and waitress service of drinks and nibbles during the film).
Funan digital mall is an ICT experience.
Wild Wild Wet water park is excellent and has a mall with restaurants attached. Bit of a drive out but only 30 mins from Orchard.
Raffles Hotel Long Bar- where you get to throw all the nut casings on the floor. There are banana trees to see as you walk through. The food is good too and the Singapore Slings unsurpassed.
Go to one of the many fish-spas and have the fish nibble the dead skin off your feet.
Tree top adventures on Sentosa- sail through the trees.
Open top buses go round Singapore plus the Duck Tour bus which is part bus part boat is good.
Look on www.sistic.com.sg to see if there are any shows/concerts on while you are in Singapore.
I wouldn't recommend Bintan- expensive but average and the ferry trip can be rough. See trip advisor for more info.
Lankawi, Koh Samui and Tioman are all nice if you are careful over hotel. Bali is wonderful if you want to go a bit further.