1 black and 1 white children

Hi! Its really a tricky question to make the little heads understand such a complex thing. But its better to tell them something relative not just a story. You can tell them that since the genes are responsible for the overall structure, complexion and everything about a person therefore might be its the reason why one is fair and the other dark. Genes decides everything of a person starting from skin color ,to taste,behaviour etc..etc.Genes are heriditary again so they may come from a forefather who was perhaps dark complexioned.Therefore genetic engeneering is such a complex study. Hope it helps.....lemme know!!