I'm almost finished with this degree @AlRRRR. I did U116, S112, SXF206, DST206, SDT306, S397 and (will do) SXE390 next year as I've screwed up picking a project and I'm so stressed about it I've decided to do that course on its own next year so I can concentrate on it!
The course materials are generally very good and even if you don't have a science background (I didn't - all my previous education was arts/languages), it leads you by the hand. I've enjoyed most of it too and the materials are a mix of hard science and social science - you'll probably have a preference for one or the other. I probably found the social science courses more interesting, but it was harder to get good marks in the TMAs, because it's all a bit wishy-washy and subjective; whereas hard science is either right or wrong, so as long as you've done the study and understand the materials it's easier to get high marks.
The tutors are variable - I had a couple of really great ones and a couple of utter duds. A major reason why I'm deferring the project course to next year is because my tutor is shit! The week-long field trip for SXF206 was great - I was dreading it and then had probably the best week of my entire OU experience. It was just SO good to be working alongside other students - at times the OU experience can feel quite lonely as it's 99% you at your computer on your own - but as a parent it really makes it easier to fit your study around your life. No way could I have managed a bricks and mortar uni with lectures at fixed times - with OU you can do the study and watch the tutorials when convenient.
As for juggling study with PT work and family, you have to be quite organised. Before you start, think about when you're going to fit your study in. I would NOT recommend that you do FT study, although some students do manage it. It depends on you, how busy your life is already, how old your DC are, how easy you'll find it study in the holidays with them around, how disciplined you are. I'm not very disciplined, so PT study was quite enough for me!