No I don't think having kids will be a disadvantage to CX hiring you, although they will probably grill you about how your wife and kids will go living in HK.
As for schooling a rough guide......
They pay 90% of the English School's Foundation rate and 75% of an international school's fee. So for an International school (I have some friends sending children to the Australian International School) they pay about $30000 per kid per year after CX give them 75%. Can change from school to school as some will have you buy a debenture then pay a different level of fees.
Housing that Flyspotter is talking about is to do with Captains working past 55 at the moment. If you joined CX tomorrow you would receive about $23000 per month and after 2 years that doubles. Slightly more if you decide to buy a house and after 15 years of having them pay your mortgage off you drop back to the base rate (about $24000 per month). Or they will pay your rent for the whole time you are in CX in HK if you decide not to buy.