World's Finest #146
SPOILER ALERT
I recall reading this back when I was very young. At the time, it was a bit unbelievable for my 7 year old self. Batman finds some pics of him demonstrating powers like Superman. The pics were taken when he was a toddler. It turned out the pics were sparked by reports of a "Superbaby" around the world. A scientist decided to take photos of how this Superbaby could have done his stunts, using trick photography. Young Bruce Wayne was selected due to a friendship between his parents and the scientist. "Flying" Bruce was done with wires, "Super-strength" Bruce with movie props and so forth.