Must one wash his hands if he touched the uncovered area of a child?[1]
This depends on the area of the body of the child. Those areas that are normally always covered require washing hands. Thus if one changes the diaper of an infant one is to wash his hands after. However those areas that are commonly left uncovered, such as the legs of toddlers, do not require washing. However there are those that are stringent by all areas normally covered by an adult.
[1] Oar Letziyon 2:44-6; See Piskeiy Teshuvos 4:23 for a list of rulings from today’s Poskim on this matter.