It’s a bird! . . . It’s a plane! . . . It’s Jayson Tatum! The Celts highly-touted rookie dressed up as a superhero during a visit Monday to Boston Children’s Hospital. As you can see, the 6-foot-8 forward from Duke put a smile on the face of young Whitney, a patient at the hospital. In reality, Tatum can’t fly, but the C’s are hoping he can jump high enough to at least grab a rebound or two, something last year’s team had trouble doing.