What side hustles have you personally seen work pretty well?
Corporations taking over side hustles seems to be screwing over people, since they take such a large cut and flood the market for that hustle.
But the ones I've personally seen people do that work pretty well (in USA) are:
Stay at home mom watching another kid (legally dubious depending on state/situation. But I ain't no narc.)
A neighbor of my mom's sends out a menu saying what she plans on cooking each night for that week, and for $X will deliver you some as well (Legal in Utah due to special laws, other states could be dubious. )
People who go pick up free furniture that is pretty trashed, and then refurbishes it and sells it. Or people with trucks who are like "Will deliver furniture for $30 in X area" is also pretty life saver for people without cars/trucks. Was able to get a super cheap/nice coach because of this.
People who just flip free stuff or stuff from thrift stores without doing any improvements annoy me greatly though. We broke and you're just driving up the price!
None of these generate a ton of cash, but I like that they take very little up front cost, aren't disruptive, and mostly take labor.
So a baby sitter baby sitting and the home of the child is completely legally fine. If you are doing it at your own home, or watching unrelated children, it can be iffy.
the fact pattern you provided mother watching another child with her own... i don't think that would quality anywhere but i did not check all the rules.
if they are running something resembling a commercial operation that would be a different story.
"For instance, most states and territories do not require an in-home child care provider to be licensed if they provide care on an occasional basis, provide care in your home, or are related to the children in their care."
Try googling it. It my state day cares must be registered and it looks like there's lots of regulations. If there is any government funding you can bet your britches there are inspections.
My state will subsidize child care for parents under a certain income. Nobody is saying anyone will get in trouble for babysitting family members. You could simply Google it and save yourself some typing and a whole lot of embarrassment