Most likely, as more than half the households in America right now have a parent-in-law as one of the decision makers rather than the natural parents of the child.
If you've taken on the responsibility of father or motherhood via the contract of marriage, then you taken on ALL the responsibilities associated with raising children and looking out for their well being and welfare.
You can't just have one bit of the job... the in-law parent has the WHOLE job.
(I'm sure that if the child "messed up" and got in trouble with the law under one of those laws that prescribes punishment for the parent instead of the child, that an in-law parent would be just as liable for punishment under that law as a natural parent... hence, if you have the responsibility, then you have THE WHOLE job.)