It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Sprinkling water over the urine of a boy is sufficient, and whatever the urine of a girl touches should be washed." Qatadah (may Allah have mercy on him) says that this ruling is until they begin to eat and drink, and when they start eating and drinking, then whatever either of their urine touches must be washed.