What draws so many people in to comics is the idea of peeking inside a world where we're all just a freak accident or a magic ring away from soaring through the air. It also helps that funny books are an environment in which writers can craft tales where literally anything can happen.
However, just because you can do something, doesn't necessarily mean you should and that is often the case when trying to change iconic characters.
Over the course of decades of stories, it's only natural that writers would occasionally want to shake things up to keep characters from getting stale. The problem is, so often they completely dive off the deep end and try to reinvent the wheel, with results more disastrous then that attempt to mix metaphors.
Changes will be made that completely undermine the whole point of a hero, or maybe they'll get bizarre new powers that don't mesh at all with who they are. Heck, sometimes even a simple change of costume can completely derail a character.
And then other times Batman gets turned into a toddler.
Writing Batman comics in the 1960's was a tough gig. Comic book plots were usually wrapped up in one or two issues and so writers were always scrambling for a new way to mix up the formula of "Batman punches bad guy and saves Gotham from death rays/Joker gas/having to acknowledge Polk-Dot Man's existence". It was a time when any plot was acceptable as long as it filled up pages. And that's how we got Bat-Baby.
Every part of this story is an amazing adventure in lunacy. Batman and Robin chase down an evil scientist with the least intimidating name ever, Garth. Garth hits Batman with a ray gun (literally how 90% of 60's Batman comics started), which de-ages him to a child. We then get the most unintentionally adorable panel ever, of Robin carrying a baby Bruce Wayne in his arms, wrapped in a far too big Batman costume.
Bruce then decides to fight crime as Bat-Baby (because apparently 5 year old Bruce Wayne is still ripped) until he tracks down Garth and is restored to full-size.
Unfortunately we never get an answer to the issue's most burning questions like "Did Batman just have a child-sized outfit lying around the Batcave?" and "If he did, why doesn't he have trousers? Was it to distract villains with his overly muscular child legs or does he just really like dungarees?".