Because they make your or your children's day.
I was thinking about this today when DD was waving madly at a bus driving by, and a woman waved back. Thank-you, woman. DD was very happy.
- People who wave from busses/trains etc
2. People in shops who give your children something free (balloons, slice of luncheon meat, bit of deformed criossant etc)
3. People who smile/wave/make funny faces/chat to your child in a queue, or on a bus, train, plane etc.
You are all brilliant human beings. Add to the list!