Parents are not allowed to inflict physical marking or mental harm
A cross-party group of MPs has failed to force through a ban on smacking children in England and Wales.
Led by Labour's Kevin Barron, the campaigners opposed the current situation allowing parents to use the practice as a "reasonable punishment".
Some 28 MPs signed an amendment to the Children and Young Persons Bill, but this was not discussed.
The government said it had tightened up protection for children but opposed making smacking a crime.
Under a tightly drawn timetable, MPs had just four hours to debate the legislation, and that was taken up with discussion on long-term residential placements and fostering issues.
Mr Barron, chairman of the Commons health select committee, said: "It was always a long shot because the bill was not about the punishment of children; it was about the protection of children."
He added: "The issue won't go away. This is something many of us feel concerned about."
The amendment, signed by 28 MPs, called for children to have the same protection against assault as adults.
Campaigners said 111 Labour backbenchers had signed a private letter demanding a free vote on smacking, with some warning they were prepared to defy the whips if ministers did not back down.
But the government and opposition front benches said they wanted to focus on the main functions of the bill, which do not include dealing with corporal punishment.
Prime Minister Gordon Brown's spokesman said the government was clear on the need to safeguard the interests of children but did not support an all-out ban on smacking.
Children's Minister Beverley Hughes said, while it did not condone or encourage smacking, the government did not want to criminalise it.
She said: "If we put a ban on smacking into legislation it would mean in practice that a mother who gives her child a mild smack on the hand when they refuse to put back sweets picked up at the supermarket checkout could end up facing criminal charges."
She added that a survey suggested fewer parents were smacking children and the law had already been tightened to give children greater protection from assault.
The last attempt to impose a full ban on smacking was defeated in 2004, although 49 Labour MPs rebelled.
A compromise was agreed, tightening the law by outlawing punishment which left physical marks or caused mental harm.
Last December, Northern Ireland's children's commissioner failed in a High Court attempt to force the government to outlaw the physical punishment of young people.