Best of luck to you in your studies! I'm just checking out Mothering before getting kid #2 to school and then finishing my paper for this semester. I am in a paralegal certificate program currently. Do my kids love me being gone an extra evening - not really. But they know I'm doing this to further my career. And they were too young to remember when their dad was gone 2-3 nights per week doing his school. They are in school during the day, so I just try to squeeze in studies around my freelance work that I do at home (approx. 30 hrs./wk. plus/minus depending on the week), housework, and a babysitting trade after school. DH is a teacher, so someone is usually working part of the time in the evening anyway, and they are doing homework, etc.
I grew up this way, too, with my mom in night school, and I think it's actually ultimately a positive for the kids, both money-wise if you get a better job & motivation-wise seeing you trying to improve your situation.
PS I can only manage one class per semester & I do not take online classes (finally gave up on that after trying a couple and never following through. The face-to-face interaction with other students and profs is what I really like.)