I'm studying with the OU fulltime this year and combined with my Saturday job and my two pre-school DC I'm absolutely drowning. H and I are in the process of splitting up which doesn't make things easier. I've got three assignments due in the next 4 weeks and I'm so behind in all modules I just want to curl up and cry. I struggle with anxiety on top of everything else. But I know that hiding and crying will just make the problem worse. I didn't get half as much planned in the xmas break as I'd planned to.
I am studying OU part time, and work full time. I have no DCs, so not in the same situation as you, but studying as well as real life is hard.
I had MH issues and got really behind with my module. I spoke to someone lovely at OU and explained all that was going on, they made helpful suggestions.
Something I have also done in the past (this is my last module after 6 long years) is simply to defer. If you do this before the end is March, they bank your money (and your assignment grades if you want) and you start again next year. This made my life easier as I was then free to do the module in my own time (as I already had the box and remembered to download all the stuff from the module website), catching up when I could and then the next year would "only" (ha ha ha!) have the assignments to do. This made it a lot more flexible for me to fit it around my job.
Phone them and talk to them, they really are lovely.