It would be added to, not replace, all the payments and allowances and credits now extant. Those stay at home moms, the ones who want this type of stipend would exult in the new ability to pay for an abortion or three every year and drink a lot more sodas or wine and do a lot more drugs.
You sound like my uncle whose #1 complaint in life was that there was no legal mechanism to force his ex-wife to actually spend his child support payments ON THE CHILD.