Disabilty Tax Credit

I don't know how many of you know anything about this but it's worth a shot. My son was dianosed with autism in 2005. This year on my taxes I should be able to do what is called a disability tax credit and get some money back. I also maybe able to get some back pay. Can anyone tell me about how much I should expect to get back? I mean roughly because I know without knowing our actual income it's hard but we made around $15, 000 this year. Also I am starting to save money for the kids when they get older. Right now their ages are 4, 2 and almost 1. I want them to have enough saved so that when they decide to go to college or university or if they decide neither they will have enough for a down payment on a house or to buy a car. How much do you think I should be putting in each of their accouts each month? They are just basic savings accounts.