My nephew started to get yellow skin all over his body! He is 10 months old now and he had it for 6 months.?

Easy. This is what is known as carotenemia. Carotene is a precursor of vitamin a and the yellow color comes from a build-up of carotene from the ingestion of yellow vegetables like squash and carrots. It is totally harmless and you can differentiate it from jaundice by looking at the whites of the eyes. If they are also yellow, it is jaundice. Decrease intake of yellow veggies.