I think in this day and age of always being available, we've lost the ability to understand the concept of a village and of chilren being cared for by other people, possibly somewhat differently to how we would care fo rthem, but always with good intentions.
I mean, where do you draw the line? if she fell and needed an ambulance do you call the parents first? If she's cut herself and you want to give her first aid, do you call the parents first?
What about for other things? if she behaves badly, do you get a call before she gets told off? If the children want to play in the paddling pool and she doesn't have a swimsuit do you have to get a call to get permission for her to play in her underwear?
30 years ago, a parent looking after your child while on a sleepover would 100% be considered the responsible parent because there would be no assumption the actual parent could be reached.
I also wonder if people who are so anti this have a 10 year old. becaues of course a 10 year old is perfectly competent to ask and explain about basic medications, allergies etc. I tell people about DD's lactose intolerance but emphasise that it's mild and that frankly, they should feel free to be guided by DD - if she wants to risk a stronger reaction, that's on her.