When we brought our son Dominic home from the hospital, his older brothers had a lot of questions.

"Mom, what is Down syndrome?" Max asked.

"Down Syndrome is what happens when a person has one extra chromosome," I said.

"But what is a chromosome?" Max asked.

"A chromosome is a set of instructions. You know how sometimes I tell you something to do and then your sisters come in and boss you around and each of them tells you what to do, and things get confusing?"

Both my boys nodded vigorously.

"Well, chromosomes tell a baby how to start growing inside the mom. When there are too many instructions in there, things can get confusing."

I pulled them closer.

"Open your hand," I told Max. "You see those lines all over your palm? See how you have one here and here?" Max nodded. Atticus took off the baseball glove he'd been wearing all afternoon, unfurled his fingers and looked down. I traced the lines on their hands then showed them mine. All of us had several creases across our palms.

"Look at Dominic's hands, and tell me what you see," I said.

Max reached down and unclenched the baby's fists. First one, then the other. "There's only one line," he said.

"Right," I said.

"Only one. That happens with Down syndrome. Somehow the instructions for how many lines to put on a hand got a little mixed up.

"There are other things, too," I told them. "See how all your fingers are straight? Dominic's pinky fingers have a curve in them. His ears are lower than yours, and his eyes look a little different than yours do, too. Now do you think that is a problem?" They shook their heads.

"Did I ever have Down Syndrome?" Atticus asked.

"No, it doesn't work like that," I told him. "Either you have it or you don't. If you have Down syndrome, you have it for your whole life. Dominic will always have it, and you never will."

Atticus nodded. "Oh," he said.

"There is one other thing that you can't really see right now." I continued. "Dominic's muscles are a little bit weaker than yours were when you were a baby. He might have trouble learning to do some things that you can do, or it might take him a little longer to learn to do things. You can help him with that."

"Yeah, because I'm strong," Atticus told me. He flexed his muscles to prove his point.

Max saw that as a challenge, and soon they were comparing biceps and assuring me they were very, very strong. The older boys hugged me and ran out to play baseball. I held the baby, and looked forward to the day when the older boys would teach Dominic to play too. After all, he's just one of the boys.