Blame the dad.

Father's are responsible for the behavior of their household. They will be held accountable to God if the wife or kids do wrong. The sin nature is passed from generation to generation by the father not the mother (otherwise Mary would have passed it to Jesus). I don't know if it is part of the X chromosome but I doubt it. For the chromosomes are part of the flesh and the sin nature is a spiritual thing. Many people think that babies are inocent and only learn to be bad from thier environment but that is not so. Anyone with a two year old knows you don't have to teach a child to be selfish and rebellious. and a warning for those struggling with the "Terrible Two's". Just as 14 is 7 times 2 a 14 year old takes as much effort to control as 7 two year olds.
When a mother has a baby she makes little adjustments to be a better person. When a man becomes a father he makes huge adjustments -- he has passed some of his evilness down to the next generation.