It's the best feel-good book I have encountered for ages. It's hard to precisely say why, but somehow, the combination of the story, the rhyme and the illustrations is just spot on.
The illustrations are wonderful: bold brushstrokes and clean colours, chunky dogs with shiny fur and floppy ears and most of all perfectly rendered expressions of emotional states: the flying Sid and family simply ooze elated happiness. Sad Sid is *really* sad which shows both in his expression and posture. His dad approaching worried Sid is a picture of loving parental concern.
The rhyme is simple, bouncy and good for reading aloud with enough repetition to emphasize but not too much as to bore.
The message or moral if you wish is, of course, of believing in yourself and your own experience against the opinion of authority (the teacher) and the peer group. The family is warm and caring, and of course, flying is an age-old allegory for joyful freedom of personal expression.
Apart from reinforcing self-belief, the book would provide an excellent basis for talking to your child about different feelings and reasons for them as the drawn characters have such clear facial and bodily expressions.
All in all, a fantastic picture book, with good rhyme, great illustrations and a huge feel-good factor. I would say it's suitable from about 2 years old, but a 3 to 5 year olds would appreciate it most.