Travel with kids forum

Hi,
we are planning a 4 month trip around SE Asia next summer. I know we're going to be in monsoon season, but the school would only agree to the trip if it took in the kids school holidays and didn't cut the start off the new school year in Sept. My question is where to go. We'll probably fly from the UK to Bangkok in early May and the only complete definates are Angkor wat and a beautiful beach (somewhere must be sunny??)I want to visit either malaysia or the phillipines for about 3 weeks and indonesia for about the same. So we're talking about 10 weeks to travel the rest of the area. We love temples, history & culture. We would also maybe like a short easy jungle trek ( the youngest will only be 8)We would like to break up the cities and towns quite regularly with beaches, but nothing too touristy. We love laid back towns and beaches and would only really want to stay in big cities for 2-3 days at a time - or enough to see the "must sees". The kids are well used to travelling and roughing it quite a bit - we travelled around North Africa for 8 weeks 3 years ago and India for 14 weeks last year on a tight budget. We'd prefer to spend more time in cheaper areas, and nearly always in budget accomodation - so then we can splash out on fabulous experiences, meals and hotels every now and then!
So we're not looking for much!! lol I just thought I'd give as much detail as possible so that someone may come up with some ideas for us. Any suggestions of an itinery or things we shouldn't miss would be very much appreciated!
Thanks in advance
Kula