A 21-month-old girl was kicked by a stranger in York while she waited with her childminder to cross the road.
On hearing her cry, a man in front of them turned around, walked a couple of paces and kicked the baby in her stomach. She suffered a "minor external injury", said police.
A woman with the man immediately apologised and said the man had a behavioural condition.
The incident happened at around 9.55am on Wednesday at the pelican crossing on the junction of Lendal Bridge and Station Avenue.
Police are appealing for the man and woman to come forward and to anyone who witnessed the incident to contact them.
The man is described as aged between 20 and 35, of heavy build, approximately 5ft 6in tall and with thin hair. He was wearing dark trousers and an older style jumper with stripes. His shoes are described as big and he appeared to be dressed in clothing which an older person would wear.
The woman with him is described as around 5ft 6in tall, aged in her early twenties, of slim build with dark hair.
Witnesses are asked to phone PC Craig Appleby on 101 or to email firstname.lastname@example.org