Liam couldn't be happier. He's off to kindergarten, where he's going to make a million new friends and learn a billion new things Mom is worried about Liam going to school, but Liam knows he'll be fine. He has his oxygen mask and his medication for lunch and snack time. Plus, he knows he's strong as a tree. You see, Liam has a great big tree in his backyard. Mom says trees need lots of oxygen from the air, just like his lungs. And they need...