Odd dilemma

This morning I was driving my daughter to school, running late as usual, when I saw 2 little boys on the footpath. The smaller was sitting and crying and the bigger was trying to pull him up.
I turned around to see if they were ok and it turned out the little one had fallen over and skinned both his knees quite badly.
The school is down a cul-de-sac and they still had a way to go before they got there, so I suggested they jump into the car and I'd drop them up at the office so they could get his knees cleaned up. (typical, I normally always have wipes and plasters in my bag but not today!)
Good deed done, I dropped my daughter off and went on my way.
As I drove off though, I was thinking about how I would feel if it had been my children.
I always tell them to never, ever get in anyone else's car, no matter what.
The little boy is in Ella's class at school, so I and she would have been familiar to him, but he doesn't know me really, and his (I'm assuming) brother definitely doesn't. But neither hesitated about hopping in with us.
Thing is though, I wouldn't have wanted my poor kid hobbling up the road bleeding and crying and no one to help either, which is why I stopped in the first place.
It is such a tricky thing these days. You train your children to be so careful and cautious of strangers, but in a completely random situation like that when you're not there to be mum, you need to be able to rely on the kindness and trustworthiness of people too.
Sorry this is such a jumpy, rambly post.
I guess I just wanted to get other opinions and takes on this as I was planning on having a bit of a talk to my kids about it this afternoon but when I was going over it, I was a bit confused as to how to approach it!

you may find the only reason they got in your car was because the kids "knew" each other from school. i personally would not want my kids to get in a strangers car, even if they had hurt themselves. i would have asked if they were ok and waited for the little boy to be ok to carry on walking and would probaly have informed the school when i got there of what had happened also. Even if someone is just helping you can never predict what will happen in the car so i think it is best to just stick with the not getting into cars rule, ever.