full time undergraduate and childcare?

Hello, I'm due to start an undergraduate Degree this September, I have a 3 year old son. I'm trying to think about the best option with childcare (Im a single parent with little support so nursery/childminder is the only option really)
I won't be working as my course is full time, What are the options for paying for childcare if you dont work? how does the childcare grant work? nursery 5 days is going to be over £900 and I think I get 85% paid for by UC...just wondered how it all works? TIA