They are Wandsworth, Richmond, Kingston, Sutton, Croydon, Merton and Surrey.
Their leaders have written to Labour’s Wes Streeting after Wandsworth announced last week it was now challenging the move.
The decision was made to move children’s cancer services from St George’s in Tooting and The Royal Marsden in Sutton in March by the NHS.
They are due to be based at the Evelina London Children’s Hospital in Waterloo from Autumn 2026.
But the councils say they want the decision reviewed by the new government.
The letter signed by all seven council leaders represents 2.7million people across their constituencies.