While I wasn't a single mom, but I did work full time during LPN school and a non-traditional student (I was 38 when I started). It wasn't easy but it can be done. You need to be sure you have a support system, come up with a plan to keep you organized and a way to balance your children's wants/needs, school and work.
I'm thankful for my husband. He stepped right up when I went back to school. He cooked, cleaned, did laundry, did the grocery shopping and did all the things that were normally on my plate. My children (ages at the time just turned 6 and just turned turned 15) also helped out greatly! Your older children can help out in small ways. Explain to the older ones what you are doing and why, how it will better all of your lives when you graduate and are able to secure a good paying job etc.
Keep your eye on the prize...don't give up. I won't lie and say its easy, but it's also not impossible
Don't go into this with a negative attitude...go in with the I can do this, WATCH ME!