This week at Liverpool's Alder Hey children's hospital, two-year-old twins Katie and Aimee both have pre-operation tests for holes in the heart. Sixteen-year-old Nadia and ten-year-old Louise, who have walking problems caused by cerebral palsy, return to the hospital to take their first steps following operations on their legs, and casualty nurse Mike Callaghan deals with a teenage girl who has swallowed a 50 pence piece.