I'm curious what "unemancipated child under the age of twenty-one years" means. Normally, "unemancipated" would mean a legal adult and, AFAIK, that means anyone aged 18 or older. If that's the case, "unemancipated child under the age of twenty-one years" would be redundant.
Under New York State law, both parents must financially support their child until the child turns 21 years old. Child support also includes providing health insurance coverage until the child turns 21 years old.
If the child is under 21 and married, self-supporting, or in the military then the child is emancipated and the parents don't have to support the child.