You will probably have a freshers week or even 2.
They are a mixture of social events and useful information. Go to the inductions for the library/learning centre and the academic support sessions.
There are usually short 1 or 2 day courses you can do for things like research or essay writing - go to them, you won't have chance in year 2 and 3.
The fresher's fair is where you pick up loads of freebies, pens, security markers etc. It's worth looking at getting a student bank account but check what they are offering.
Have a look at any societies you find interesting, sometimes there are ones for single parents / mature students.
Don't bother paying for an NUS extra card. Most places that do student discounts will accept your ID.
You will get your timetable the first week but this might only be for 1 term or 1 semester. You will probably get a reading list for each unit/module. Ask your tutor which one or two books is essential and consider buying them.
Get an academic diary - might be a freebie for the uni but mark in it your timetable and time to spend with your children.
You are unlikely to have any lectures Wednesday afternoons so that might be the day to take the kids to the park.
One of my cohort used a post it note, the note was put in every week of her diary and that was her 'me tie' she could move it to a different page but had one day blanked each week.
Good luck and enjoy yourself.