A new strategy aimed at increasing support for organ donation from children is being launched by the NHS.
Children can wait twice as long as adults for urgent heart transplants because of a shortage of suitable donors.
Siblings Grace and Freddie Fincham from Portsmouth are patients at Great Ormond Street Hospital in London.
Grace was given a new heart but now her brother needs one too.
Produced by George Henton and Claire Brennan
You can see the full report on Inside Out London on BBC One at 19:30 on 4 March. Or catch up on the iPlayer.