Mom allows her 13-year-old daughter's friend to spend $100 on Roblox gift cards for her and her daughter, doesn't ask her daughter's friend's mom for permission: 'Why would her mom do that?'

She should never let her have a play date at their house again. 

A good rule of thumb when deciding whether to let your kid hang out with another kid without you supervising is not to agree to a hangout before you've met the other kid's parents. You might not be able to tell everything from a brief interaction with little Billy's mom, but if you have an implicit feeling that you can't trust her with your kid, you shouldn't let him have a sleepover at her place. 

You can't control what another parent does in their house, so allowing your kid to spend time at someone else's without your supervision isn't a small decision. Many parents forbid sleepovers and playdates at other houses altogether, fearing the worst. While that's one way of mitigating risk, a better way might be to become friends with your kid's friend's parents. If you can hang with your kid's best friend's mom, and make her your best friend in turn, then you can all hang out together, and neither parent is sitting around at home worrying about what could possibly be happening without their knowledge. 

There are levels to crossing a line when you're watching over someone else's kid. Is it wrong to serve your friend's kid macaroni and cheese when they're not allowed to eat it at their house because their mom thinks it's unhealthy? As a parent, would you serve it without asking the kids' parents' permission first? Would you request permission if you had already made the food and the kid didn't tell you that it was forbidden in their household until after they'd taken their first bite? It isn't always an easy question to answer, but when it comes to other people's children, I would almost always err on the side of caution.