This has all been resolved now. The kid in question got a new bike today, with correctly oriented forks. Not that he seems to ride much I dont think, prefering a scooter and little ramp. Turns out that they are more talkative than I thought so probably would have been OK, I guess lesson learned, judge, book, cover etc.
Don’t mention it to the kid. He will probably just think you’re a weirdo. Which you’re not. Kids that age are a bit awkward. Certainly don’t offer the kid to fix it. Need to be super careful around kids.
I would politely bring it to their parent;
“Excuse me; I’m Martin. I couldn’t help but notice that your child’s bikes forks are on backwards. Hope you don’t mind me mentioning but it’s a bit unsafe. Thought I should say something. “
You can “You’re welcome to bring it over if you need help fixing it “