Sry to be the bearer of bad news (and to be so negative and blunt), but virtually all of the international schools' deadlines have already past (due Oct/Nov 2009) for entry for Aug/Sep 2010 Reception classes (4yrs olds starting in Aug/Sep 2010).
They are conducting interviews right now (Dec-Feb/Mar) and will be making their decisions in March/April.
Sounds like your kids are born in 2006 so they would be eligible for Reception class of 2010/11.
As we have discovered, unless you get into the Reception class, it is extremely difficult to get into the int'l schools unless a kid moves and a spot is available. Kids move up to the next grade up each year. In other words, the key entry years are Reception Yr and Year 7 (year 7 b/c they usually add another class). Further, similar to the London schools you mention, the probability of acceptance in the elite int'l schools are 1 in 5/6 kids applying.
I think you have two options: 1) call each international school you are interested in ASAP and see if they are willing to 'bend' the rules. Some are VERY strict on their deadline, however, they may make an exception because you are applying from 'overseas'. Further, maybe your husband's company is offering him a coporate debenture at a certain school? OR 2) as the other posters have mentioned, the ESF school system does not start Yr 1 applications until Sep 2010 for entry Sep 2011 - so you have time on this front.
Take a look at a post by a user named "Mammia 1" (spelling?) re: timing and his/her regrets re: international school applications.
Again, you need to get on the ball and start calling ASAP. Also, someone mentioned Kellett school (a UK based school in Pok Fu Lam) - you need to call them ASAP. They may take your application as they are run slightly different - chk their website out.
Again, apologies to be blunt, but learned some of these things the hard way and don't want it to happen to other parents.