Memoirs of an Imaginary Friend

Budo is Max's imaginary friend. But though only Max can see him, he is real. Budo and the other imaginary friends watch over their children until the day comes that the child stops imagining them. And then they're gone. Budo has lasted a lot longer than most imaginary friends - four years - because Max needs him more. His parents argue about sending him to a special school. Then Max mysteriously disappears from the school. Budo knows he must find him and rescue him.