Eight people who were arrested on suspicion of involvement in the abduction of the three boys have been bailed to a later date.
Met Police Commander Jon Savell confirmed more than 100 officers are working to find the three children.
Commander Savell said officers are “growing increasingly concerned about their wellbeing” but added “we do not believe at this time there is any immediate risk to their physical safety”.
In a statement, he said: “Our absolute priority at this moment in time is the welfare of these three children.
“They have been taken from a place of safety and we are growing increasingly concerned about their wellbeing, particularly as we remain in the midst of a global health crisis.
“While we do not believe at this time there is any immediate risk to their physical safety, their location, access to accommodation, healthcare, and other provisions is entirely unknown.