When a child is born with Down Syndrome there is really no telling how "high functioning" they'll be. As a new parent, it's scary wondering how much your child will be able to learn, when they'll begin to understand you or even be able to communicate themselves. Just like regular kids, kids with DS will learn at different paces. What I'm trying to say is that you can't lump Down Syndrome kids in one category. Some are further behind than others, and some might be right on track with most baby mile stones.
I remember asking the doctor in a million different ways, how soon Welles would start doing "normal" things. "When is it apparent how high functioning he'll be? Will we be able to measure his disabilities within the first year? When do most DS kids start showing signs of being behind?" etc... You get the point. I was eager to know what his learning curve would be like. Funny enough, as time passes I find myself not really worried about those things; it's just fun to watch him learn no matter what the pace is.
Back to the clapping. When I say "yay" and Welles starts clapping, this means that he is connecting words with actions. And he is repeating things he sees us do - also great for his brain development. Every parent gets excited the first time their child does things like this. I remember the excitement when big sis started clapping and copying, but since we weren't sure when to expect these things from Welles, we celebrated that much more. He is putting the pieces together and showing us that he can do it! His brain is working just the way it's supposed to. How beautiful it is that families of children with special needs get to jump for joy over these milestones.