Batteries

We were in the "sky lounge" this morning (an indoor playspace that looks down on the big gym in our school and my kids were watching an older group of special needs students play in the gym. One girl is in a wheelchair and a little boy asked me, "What's she doing?"
Me: She riding in ther wheelchair.
Him: Why?
Me: Because she needs that chair. Her legs don't work like yours do.
Other little boy (who is fully able-bodied): My legs don't work either. The batteries in them broke.