I'm tired of seeing these moms ride with their kids in the bottom of the shopping cart. I think I will tell off the next one I see.
Really? What's wrong with the son riding in the bottom of the cart?
It's a shitty thing to do.
Mind your business, they're not bothering you so don't bother them. The mom just wants her son to have fun, there's no reason for you rain on all of that. You don't know this mom and her son, so you can't be rude and parent for her.
Isn't this what we should do, tell people what is bad for their kid?
If the store thinks that it's unsafe to do, an employee will talk to them. Otherwise, it's best to just mind your own business, as they're probably not going to stop just because you yelled at them.