Doubling.

Lots of kids ride behind their parents like this.. They are confortab;e doing it.. He's not hanging on for dear life. He's checking out for oncoming traffic just like mum. It happens on motorcycles and bicycles that kids sit like this. I saw one setup today where a small seat was built onto the back of the handlebars for an infant to sit in. That was so three people were able to travel comfortably on the one bike. The ingenuity of the Chinese amazes me.

EDIT:. If dad is there too, he would be in the rider's seat, the boy would stay in the same place and if you notice, the seat behind the boy is big enough for mum to sit on as well.