(Yes, I have kids. Yes, my kids play. Yes, I dislike when people are exceeding the speed limit by a lot.)
I'm all for speed limits and going the speed limit, but I honestly don't feel like the road is any safer for someone going 5mph vs. something going 10mph (again- legitimately going 10mph, not exceeding that). I can't imagine that reaction times or anything differ that much between the two.
5mph is mindnumbingly slow. I literally have to ride the brakes on my truck to go that slow.
Have a speed limit, make it 10mph, and enforce it. But 5mph is too slow.