Peter, the Knight with Asthma by Janna Matthies illustrated by Anthony Lewis
Young Peter is a brave knight who battles fire-breathing dragons, rescues tigers, builds igloos, but has to take breaks to use his rescue inhaler. His mother, realizing that Peter needs to use his inhaler far too often takes him to the doctor where he is diagnosed with asthma. During Peter's appointment with the doctor, he is introduced to some new items-- the peak-flow meter, and a nebulizer machine-- both which will help Peter get a hold on his asthma.
I liked this book as a quick intro into asthma for a child because it shows Peter being allowed to do the same things he could do before his diagnosis. The hand-drawn nebulizer is a wonderful, non-scary introduction to treatment.