Scotland has become the first nation in the UK to make smacking illegal.
Under Scottish law that came into force on Saturday, children now have the same protection from assault as adults.
"If you see someone physically punishing their child, you can call the police on 101 if you think a crime has been committed," the Scottish government confirmed in guidelines outlining the new law.
Previously, a parent or carer who smacked a child had recourse to the defence that they had used "reasonable chastisement" in striking them.
Children's minister Maree Todd MSP said: "I'm very pleased that Scotland has become the first part of the UK to legislate to ensure that children, without exception, have the same protection from assault as adults.
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"This outdated defence has no place in a modern Scotland. It can never be reasonable to strike a child," she added.
According to the BBC, Scotland is the 58th nation across the world to ban smacking. Sweden led the way by making it illegal back in 1979.
Under the Children Act 2004, smacking is still legal in other parts of the UK provided it is deemed a "reasonable punishment".
However, Wales has also passed legislation to make smacking illegal, which is due to come into force in 2022.
Today's news was welcomed by the Scottish wing of the NSPCC (National Society for the Prevention of Cruelty to Children), which had campaigned for the ban for many years.
A baby born in Scotland today will never know a country which allows them to be physically punished. I think that’s something we should all take great pride in. 🏴❤️#equalprotection #UNCRC@NSPCC_Scotland @children1st @BarnardosScot @JohnFinnieHI @MareeToddMSP @Bruce_Adamson
— Joanna Barrett (@Joanna_Barrett) November 7, 2020
The organisation's Joanna Barrett said: "This law sets out in clear terms that physical punishment should no longer be part of childhood in Scotland and it marks a momentous step in making it a country where children's rights are truly recognised, respected and fulfilled."