A very worthly profession and a great investment on your part. Your being at home with your kids will make them better adults and I'm sure also statistically will make them more likely to finish college. I certainly have nothing bad to say about stay at home parents.
Well you could have two approaches. One, you could just statistically look at the increased income of graduates of various degrees vs. those without degrees and fund those degrees accordingly.
Or, you could consider all the state subsidy of higher education to be a loan. Then take any amount of income that the person later pays taxes on in excess of someone without a degree (say $40,000/yr) and forgive a portion of the subsidy based on that income tax paid.
We can figure this out.
-Robert