I think I harmed a kid when I was a delivery driver.
What did you do to the kid?
A mother told me her daughter had health issues and she shouldn't drink caffeine, so I hid a pack of caffeinated soda among the cases of decaf.
If a mother tells you not to let her kid have something for a medical reason, it is wise to abide by the request. You could put the child in a dangerous situation if you give her something she isn't allowed to have.
The kid can drink the soda, she won't overdose on caffeine.
She's unlikely to overdose on caffeine, but you don't know what the actual effect of caffeine would be. It's not okay to ignore a health concern just because you don't think it's important. I hope you wouldn't do something like this again.