Families in Golders Green have been told to take precautions after a stranger attempted to abduct a child on Tuesday - the second incident of its kind in the past week.
According to the community volunteer security patrol, Shomrim, a man tried to persuade an eight-year-old boy into his car by offering to drive him home. The boy ran away.
This followed a similar incident, believed to involve the same man, last Friday.
"Police have been working with us," said Shomrim chief executive Gary Ost. "We are in the process of checking CCTV footage to find the vehicle. So far, there is one male suspect."
Shomrim has been advising local schools and parents over the need to be vigilant.
"This does not mean that children should not go out or play outside," Mr Ost said. "We just want parents to make sure their children are aware of the dangers."
A Metropolitan Police spokesperson said: "We are increasing patrols in the area and will be supporting the families, as well as investigating as far as we can."