There is NO NEED to RESORT ON VIOLENCE upon a child...not even by parents. It just need MORE public awareness, elected govt support and wholesome education to be taught at schools, because violence only begets violence, more so to a child in their formative years, and would only grow up believing that violence AS A FIRST RESORT would RESOLVE issues.....
Kids are only naive growing adults, and THEY are the FUTURE OF HUMANKIND. Violence and Wars can only be used as a last resort, when all diplomatic and every avenue of means failed, in order to achieve PEACE, stability and the very values that all Humankind shares, as PEACE is an irony, as it sadly will need sacrifices and efforts to defend it.....
As for a seemingly wayward child misbehaving in public, the best approach is just to talk to them gently, not harshly, and if it fails, then take a photo of the harm they had done and send it to the relevant authorities to handle, but do not, DO NOT, ever touch a child.
Should the child be accompanied by parents, then just a mere calm and diplomatic talk to the adult parents would suffice. However, should the parents turn nasty or violent, then take a picture as evidence of violence of being inflicted by others upon oneself, and let our authorities handle the rest. There are cameras everywhere, on streets and even on an MRT train that would help as supporting evidences.