Yip, I've seen signs saying "slow kids", and one where slow had been crossed out and replaced with retarded.
I was once told off by a neighbour when I drove home a little faster than he liked. Him: "What speed do you think you were going?" Me: "About 40." Him: "40 for goodness sake!" Me: "It's only 10 over." Him: "There's kids playing in the road!" Me: "You shouldn't let them do that, shall I call social services and have them taken away?" Him: Blank expression, then walked off.