My young child is confused about whether my co-wife's children are his cousins or his siblings. How do I explain?

Explain in simple words: they are siblings because they share the same father, not cousins. Young children understand relationships through everyday examples, so avoid convoluted explanations. Try saying it briefly, such as ‘He's your little brother, not your cousin, because we have the same father’. Show a photo or a simple drawing of a family tree so that he can see where everyone fits. Avoid belittling terms when referring to the siblings in the other home. When he is older, explain the family arrangement more fully. For now, it is enough for him to understand one important thing — his siblings in the other home are part of his family. See children in polygyny.