I’ve seen this many times. There are many children that don’t have blatant resemblance to their parents. They might have a few similarities, but they are not easily distinguishable.
I am not well-versed in the subject, but I think that it has something to do with the environment in which he or she grows up. Right from the beginning of their lives, in the wombs of their mothers, extending to their early years, and so on.
I’ve read that the environment of the womb affects a child’s development. Things like the mother’s diet, psychological well-being and even blood pressure or blood sugar levels affect the baby.
Obviously, the environment of the first and subsequent years of a child’s life affect development, and may cause the child to look different from his or her parents. Diet and climatic conditions are just a few examples.