It can happen for all sorts of reasons. Perhaps a child has just tried to dash out into the road or stick a fork into an electrical socket. Maybe they are willfully ignoring their parents' instructions - or maybe their parents have just reached the end of their tether. So the child gets a smack.

Perhaps not for much longer - at least in Wales, which published a bill last week that would ban parents from smacking their children.

Currently, it is legal in Britain as long as parents do not use "excessive force"; usually this means leaving a mark. This is because the laws against hitting children have an exception for parents who use "reasonable punishment", which dates back to then Victorian era. But the Scottish parliament has been attempting to close that loophole since 2017. Now Wales is doing the same.

They will be joining 54 countries which have outlawed corporal punishment for children, according to an report published last year. Technically, physical punishment violates the United Nations Convention on the Rights of the Child. The UN aims to end all forms of violence against children by 2030.

But not all parents are happy. In 2017, an YouGov poll found that only 22% of Britons thought smacking should be banned. Last week, a mother from Cardiff told  Metro that a light smack can be the "kindest way" to discipline young children who are doing dangerous things. It shows that "mum's in charge and I need to keep you safe."

Yet studies have found that smacking can make children more aggressive or cause mental health problems later in life.

Smacking is legal in the US, but last year the American Academy of Pediatrics released a strongly worded statement telling parents that all forms of corporal punishment "are minimally effective in the short-term and not effective in the long-term." Instead, it recommended more "positive" forms of parenting, such as encouraging good behaviour.

Absolutely not, say some. Discipline is an important part of raising children, but when they are young they may not respond to reasonable arguments or repeated requests to behave. If they are putting themselves in danger, a light smack is the quickest way to stop them. It is ridiculous to suggest that this is the same as abuse, or that parents should be locked up for it.

It should be banned, argue others. It is totally illegal to assault an adult, for any reason - so why should it be legal to hurt children? There are other forms of discipline that will be more effective and less harmful. What's more, hitting children will teach them that violence is an acceptable response to fear or anger. Smacking is a relic of the past. It is time to leave it there.