This is actually very common from what I saw when I was in Laos. Surprisingly, kids have great balancing abilities. I often saw them just sitting on the back of the bike without even holding on, as seen in the photo.
Oh my god, there is no safety for the kids, and where is the rules of traffic in Laos. Looking at the little girl in front the the mom, her feet could slip down any time or any minutes.
Dangerous, dangerous, indeed. No helmet and I agree serious problem will occur if there is an accident, particularly for the 2 children at the back. When this picture is taken.