The Archbishop of Wales will today warn that smacking demeans and devalues children.
Dr Barry Morgan will be speaking at a vigil service aimed at ending legalised violence against children.
He will argue that children should receive the same respect and care as adults.
The vigil service is taking place at a church in Cardiff to mark Universal Children's Day, a world day of prayer and action for children.
The Archbishop will say, "Jesus believed that children were not just an asset for the future or a commitment to be undertaken for the sake of society. They were of infinite value as children. They deserved as much respect and care as any other human being."
The service is being supported by the charities Children in Wales and Children Are Unbeatable! Cymru.
Church leaders will light candles in prayer on behalf of children who have suffered violence, and Dr Morgan will wash children's feet.
He will also say: "None of us would ever dream of smacking an adult, why should we think smacking a child is any more acceptable.
"They too are made in God's image, valued as the individuals they are. That does not mean that anything goes as far as bringing up children is concerned – but it does rule out physical punishment."
Dr Morgan is one of the signatories of an open letter from church leaders calling upon the UK to remove the "reasonable punishment" defence of smacking.
The letter says that physical punishment as a form of discipline is "incompatible with the core religious values of respect for children's human dignity, justice and non-violence".
It states: "There are no circumstances under which this painful and humiliating practice can be justified."