The aim of the study is to determine whether piperaquine plus dihydroartemisinin (DHA-PQ) is as effective, and better tolerated, than sulfadoxine-pyrimethamine plus amodiaquine (SP+AQ), when used for seasonal Intermittent Preventive Treatment (IPT) to prevent malaria in children aged 3 to 59 months in Bobo-Dioulasso, Burkina Faso and to determine the pharmacokinetics of piperaquine in children.