Tyre tread and peoples blatent disreguard

I don't get this thing about driving slower with kids in the car.

When you're on the roads you're surrounded by children, depending on the time of day. If you hit another car, what makes you think it doesn't have kids in it?

One pet hate i have, related to this, is people doing more than 20mph part a line of parked cars. Your braking distance less than two metres, is it? So if a kid steps out from in between parked cars, what are you gonna do?

Yet no doing the 70mph speed limit on a bypass when you can see a mile..?