I teach Special Education, but at the high school level. I know there are numerous resources online, but I don't have any good URL's handy at the moment. One that you might want to look into is the Council for Exceptional Children ( [url="http://www.cec.sped.org/"]http://www.cec.sped.org/[/url] ). If you join them, you will receive a monthly magazine and you can also browse a lot of information online.
One thing to keep in mind about your children (just some basics). I will tell you up front, I know little about kids with Down's. I haven't had the opportunity to work with them in the past, particularly at that young. As older students, the kids with Down's are probably some of the most fun to work with.
For kids with Cerebral Palsy, it is important to remember that this disorder affects their BODY not their mind (primarily anyway). As such, talk to them at age appropriate levels. This is a big problem with older kids with CP. People see their outer appearance and assume that they are "slow" when in most cases they are not. Many are VERY smart (above average smart) and need more challenging work, and need to be treated age appropriately. At this young age though, I doubt this is an issue.
Good luck, it'll be fun and difficult.