Where did the term side kick come from?

Question

my 10 year old asked my "why are they called side kicks when nobody ever kicks them".

Answer 1

"Sidekick" first appeared in the slang of the criminal underworld about 1906, and originally meant a close confederate or accomplice in crime.

There is some uncertainty about how "sidekick" came to mean "partner or assistant" in criminal parlance, but the specialized slang of pickpockets may supply some clues. To a pickpocket, a "kick" is a pair of trousers, and, more specifically, the trouser pockets. "Kick" in this "pocket" sense first appeared in the mid-1800s, and to this day "kick" is used as slang for a roll of bills or other stash of cash.

The side pockets of a man's trousers have long been known, logically enough, as the "side-kicks," and it seems plausible that this term eventually came to be applied to a criminal confederate who was as close to the speaker as the pockets in his pants.