I agree - OU is addictive.
Haven't done a degree as such, just a post grad conversion so only did 3 psychology courses (including child dev.) but workload was manageable so long as you are able to get some decent work done in the evenings.
I think they reckon on 16 hours a week for a 60 point course and that was about right, averaged out. Some weeks it was more and some less. Assignments can be a nightmare though - I need a long run at things - I can't get going in short snatches of time so a supportive DH/DP/family are very helpful to get some time at weekends to get properly stuck in.
You don't have to go to seminars/tutorials if you don't want to and often I haven't and not suffered for it. Their usefulness depends on the tutor ime, and whether you like their way of doing things.
Don't worry about not working with children - the OU is made for people who want to try something different.
I am currently doing an OU MSc in Psychology so I am a sucker for punishment but for me, as a SAHM and no spare cash for childcare, the OU is perfect since you can manage your studies around the children. I wanted to do a MSc (in developmental psychology as it happens) at a university 20 miles from me but had to give up on the ideas as I couldn't make it work whilst DS2 was still in pre-school - on top of the fees (which are more spread out anyway with the OU because it takes longer) I couldn't have afforded the childcare.
By the way, if you are thinking about teaching it might be better to do a subject other than child dev. I am toying with teaching but psych and child dev aren't very useful - teacher training courses seem to prefer those with curriculum subjects (maths english etc) for their degrees.