I have to say, I teach at university and I've had 'mature' students (with kids and part-time job) attending university 'full-time'. Students have to abide by the 9-5 timetable officially. Obviously this doesn't mean that you have to hang around the university campus 9-5 M-F, but it does mean that if your seminar/lecture is scheduled for wednesday 10am, you need to be there.
Of course, childcare can let you down occasionally and kids get ill etc, but in general, we expect students to be there as much as possible. We also have a 'warning' system so if students don't turn up 3x in a row, they'll be hauled in.
My point is: it's one thing to think that college may only take up 2 days a week, or 8 hours a week, but you do need to make time for studying, reading, writing etc and I hope you will have enough childcare provision for the younger one so that you don't fall behind.
One student never turned up for lectures citing childcare reasons. Even though we have the lectures online, it's much better to be in the class listening with the notes in front of you. Not surprisingly she didn't do v well at all. And childcare is not an acceptable excuse, unfortunately (well, not where I work).