The son can get a dependent work visa as the child of the mother if she has a work visa.  In order or you to petition for them, your name has to be on the birth certificate as the child's father.  If it is, then it is possible for you to get the child US citizenship through the US Embassy in Mexico.  For the mother, in order for her to get any status on the basis of your relationship to her, you must be married AND then petition for her immigrant visa/green card on the basis of the marriage.  She does not get any immediate benefits just because she gave birth to your child.