The child was left on the 491 in Enfield last Friday in a pram. Haringey Council has launched an investigation into the incident.
Passengers on the bus raised the alarm after it became apparent that the child was unaccompanied.
The child was taken to hospital for check-ups and was reunited with its foster carer who had contacted emergency services.
Haringey Council’s social services came in for criticism after the 2007 death of Peter Connelly initially known in the press as Baby P.
The Met Police said the council was working with its child abuse investigation team.
