But it did happen in Batman No. 147's appropriately titled "Batman Becomes Bat-Baby," a story so legendarily bad that it's often considered one of the worst comics of the Silver Age. It's definitely one of the weirdest, and considering that it hit newsstands right in the middle of an era when Batman went to space more often than he fought the Riddler, that's saying something. I've even had an actual request in my capacity as the world's foremost Batmanologist to figure this thing out, and I'm not even sure I can. But let's give it a shot anyway.
Our story opens with Batman and Robin dropping in on one "Nails" Finney in order to bring him to justice for a recent jewelry store robbery. Unbeknownst to the Dynamic Duo, however, Nails had added a new member to his gang: Garth, the Renegade Scientist, a name that doesn't exactly have the intimidating ring of, say, the Joker. He does, however, have a big green laser that he blasts Batman with so that he can turn him into a 4-year-old.
I have so many questions about this, and most of them can just be summed up with why? I mean, seriously: If you can shoot Batman with a ray gun, you can shoot him with an actual gun. That would probably solve your Batman problem. Hell, even if you have to use a crazy mad science ray so that you're getting your money's worth out of having Garth on the team, I can't imagine that a death ray would be any more difficult to build than a machine that turns people into babies.
On the other hand, if they'd done that, we wouldn't have gotten this ...