I worked in childcare about 20 years ago, and we charged $1 per minute late.
We had to keep two staff there, and they would split the fine.
Many times we got stiffed.
Edit: for reference, our fee was about $14/day to keep the kid, so it was a pretty stiff penalty.
Well, If the staff got stiffed on the fee "many times", and the parents were allowed to bring their kid back.. the place didn't charge $1 per minute late. They just bluffed and got called on it.
(apologies for the immediate edit, changed my wording)
> Many times we got stiffed.
I understand that you could not keep the child till you were paid (kidnapping and ransom shouldn't be a business plan!), but you could refuse them future service until they paid.