We are planning to move to Kuala Lumpur by Sept 2015.
Can anyone please advise on a good school for my 5 year old, as well as a condo (apartment to live) in one of these areas: Bangsar, Mont Kiara and Ampang
Regarding good areas of KL to settle, all three of those you mention are popular among expats. Each is a little different - and you can read up on the pros and cons of Kuala Lumpurs suburbs here. Your best option to find out about availability of apartments that suit your needs is to contact a local estate agent. You can go to the website of the Malaysian Institute of Estate Agents to find the contact details of a few options in your preferred areas.
If you want to send your child to an international school in Malaysia, it's recommended that you start applying to a number of them as soon as you can. Competition for places is high, and your best chance of securing a spot is to apply early. Have a look at this list of international schools in Kuala Lumpur to get you started.
Hope this helps to set you off on the right track. Good luck with your research and with your relocation!