Clinical characteristics of children and young people admitted to hospital with covid-19 in United Kingdom: prospective multicentre observational cohort study by Swann, OV, Holden, KA, Turtle, L, Pollock, L, Fairfield, CJ, Drake, TM, Seth, S, Egan, C, Hardwick, HE, Halpin, S, Girvan, M, Donohue, C, Pritchard, M, Patel, LB, Ladhani, S, Sigfrid, L, Sinha, IP, Olliaro, PL, Nguyen-Van-Tam, JS, Horby, PW, Merson, L, Carson, G, Dunning, J, Openshaw, PJM, Baillie, JK, Harrison, EM, Docherty, AB, Semple, MG