Teaching a 3 year old about a child with developmental delay

My daughter goes to preschool with another child with a brain injury who has a developmental delay (can't walk or talk). My daughter has mentioned a few times this other child is a baby, and I said the other child isn't but her brain is just different. I'm looking for a book or something that might help me out in explaining this if anyone has seen one? via /r/Parenting http://ift.tt/2h2xZog