Even disregarding albinism, it's possible for people of northern european descent with fair skin to have darker skinned children. For example, in a case where the parents have germ line mutations that they pass on to their child, there could be (improbably) a collection of mutations that greatly increased the quantity of melanin. However, skin color is a complex trait with many small differences coming from a large number of different genes, so large changes in skin color are very unlikely. Nothing of what I am describing is albinism, and would have been part of the process of natural selection for fair-skinned people in northern climates with less solar exposure.