How old is your youngest, have the doctors been able to tell you much yet?
CP is a bit of a mixed bag, it affects everyone differently. I was premature and quite tiny (sometime ago now though).
The great thing about children is that they don't care about the labels medicine gives to their disabilities and they can be very resilient. Having an older sibling might be a great encouragement for your youngest and help in lots of ways.
When I was growing up, I knew there were somethings I couldn't do, but most of the time, I was finding my own way of doing things.