With half of Britain's children now overweight or obese, we follow patients and specialist NHS staff on obesity's frontline. Bristol Royal Hospital for Children is home to Britain's leading childhood obesity clinic, a last resort for a growing number of kids living with extreme obesity. Following some of the clinic's most serious cases, we meet three families, all at a point of crisis and in need of serious intervention: 14-year-old Tommy who tips the scale at 146kg, and needs round-the-clock care in hospital; 5-year-old Liliana, who has an extreme appetite and is twice the average weight for her age; and 15-year-old Harry, whose hip has collapsed due to his weight.