I have a 8 year old and a 2 year old and just finished my first semester with a 4.0. It can be done.
Sometimes I would study in between classes, or during nap time, and sometimes it would have to wait until after the kiddos were in bed. The best advise I can give is to be proactive in your studies and homework. Don't wait until a day or two before a paper is due to start researching. Also, make friends with other students. We did group study guides via google docs, so we could work on it independently, but we could all see it. This really helped because large study guides were broken into manageable parts, giving me that much more time to play with the kids.
As for how to still have time to spend with kids, the thing to remember is that it sometimes your kids will have to come first. The only time I missed part of class was because I had a sick kid. I emailed the teacher that morning to explain the situation and only came in to take my test and left before the lecture. It is okay to have a real life. It is a balancing act, but you have to balance life and work when you have a full time job. I actually like being able to set a good example for my kids about what it takes to do well in school and why it is important. Heck, my 8 year old and I do homework together some nights.
Good luck to you.