Evaluating the effectiveness of a multi-component intervention on early childhood development in paediatric HIV care and treatment programmes: a randomised controlled trial von Chingono, R, Mebrahtu, H, Mupambireyi, Z, Simms, V, Weiss, H, Ndlovu, P, Charasika, F, Tomlinson, M, Cluver, L, Cowan, F, Sherr, L