Ottawa (AFP) - A 14-year-old boy and a 12-year-old girl were charged Friday with assaulting a mother and trying to steal her baby in a random attack on a Toronto street, police said.

Inspector Art Little of the Toronto Police Service called it a "unique" and "shocking" crime.

"This is a very alarming situation... (and) a major cause for concern," given the obvious vulnerability of the victim and the very young age of her alleged assailants, he told a nationally-televised press conference.

The mother was carrying her 21-month-old infant as she walked from a subway station to her parents' home in a quiet residential neighbourhood late Thursday, when suddenly she was attacked from behind.

The suspects allegedly "punched and kicked her, knocked her to the ground and demanded her valuables, cash, phone, and her baby," Little said.

"They continued to kick and punch her without any regard for the safety of the infant in her arms. At one point they even managed to take the infant from her grasp. She fought back and was able to get her baby back," he said.

The two youths, who were also suspected in an earlier purse snatching, were arrested nearby in a police sweep while the mother and baby were treated in hospital for bruises and emotional trauma.