Dalitz-plot analyses of B^0_(s) -> K_S h^+h(‘)^- (where h(‘) is a kaon or a pion) in LHCb are discussed. First, our measurement of the branching fractions of these modes is presented. It provides input and constraints that are necessary for the Dalitz-plot analyses. Then, the time integrated untagged Dalitz-plot analysis of B^0 -> KS pi+ pi- with 3 fb-1 is presented. This is the first amplitude analysis of a B^0_(s) -> K_S h^+h(‘)^- mode in a hadronic machine. This analysis allows to determine the CP asymmetry between the B0bar -> K*(892)^- pi^+ and B0 -> K*(892)^+ pi^- decay rates to be -0.308 \pm 0.062. Finally, the prospects for other B^0_(s) -> K_S h^+h(‘)^- modes are detailed.