Not a sibling or family member but a friend's teenager etc.
I've seen several posts recently asking if it's OK to leave their teenager of 13/14/15 alone at home in the evening and it got me thinking. 25 years ago my 14yo sister used to do some local babysitting but I don't think it's common anymore to leave children (especially toddlers) with teens that aren't siblings. And if they aren't mature enough to stay at home alone I don't see how they can be mature enough to look after a small child. There are some fantastic teen parents around but even the 18 and 19yos that I know (non parents) aren't particularly independent or dependable.
I wonder if it's just that times have changed in terms of safety, or teenagers aren't as mature as they used to be, or maybe I've got it wrong and people do still pay teens to babysit