You are obviously not alone :) And the answer to your question is that it's just not possible.
I'm a single mother of a four yr old (his dad has never met him or given me a dime in child support). I worked at a $10 an hour job and lived with just me and my son, no outside support, while taking 6 credit hours at school each semester.
Now I have a much better paying job, still no help with the baggae, but work more (about 60 hours a week) so have to take less hours at school. I felt like I was depriving my son of mommy time when I was gone so much or always had my nose stuck in a book, taking two classes a semester still. I realized with all the stress I was under I was ultimately just hindering myself. I never slept enough, I was always stressed out, I have no help whatsoever, and I kept getting sick; strep throat, pneumonia, bronchitis...
I finally decided that sometimes making things work means making concessions. I am only one person and I am not less of a person if I'm not mighty woman. One class a semester is very slow, but it is all I can do right now. School will come in due time. I have money to pay the bills, to run on, and can occasionally splurge on myself instead of just on my son. I decided going year round taking summer courses was also good. Plus, I have a 4.0 GPA for several semesters now since I started doing it, so it helped me become a better student.
I reccommend you take it slow and get prioritized before you take on so much. Remember that your kids will grow up and you don't want them (even though you want to earn a degree partly so they have a good example, I'm sure) to remember you as the absentee parent, or just too busy to pay attention to them. You have time on your side...make sure you stop to smell the roses, my dad tells me that all the time!
Having a degree is important, but sometimes we cannot do everything, and our work and our kids really just outrank school. I have to have a job and I have to feed my kid; those are number 1 and number 2, not necessarily in that order :) There is no shame in keeping yourself from overdoing it! You may not graduate in two or four years, but you have to remind yourself that you will get there, maybe in 6, maybe in 7, but the point remains you will do it!