Children raising children.
That worked out great for Piggy.
It's not a waste of time to look after your own children.
But it is a waste of time to look after other peoples children.
You have to have a healthy investment, and if you have an unhealthy investment in the child, then the parents should be worried and fire you.
Someone who isn't an idiot, doesn't need any training to look after children. All additional training/higher education to look after children is technically redundant. But someone with more training is going to get the job every time, but someone with more training is going to demand a greater salary, so maybe the person who will look after your child for the smallest wage will trump the superior worker?
If you were willing to pay someone a million dollars a year too look after your baby... You would expect to get your moneys worth, but if you're only willing to pay minimum wage or a fraction of minimum wage to an undocumented worker, shouldn't you be terrified that you are getting your moneys worth in dedication and professionalism?