GO FOR IT! I left school without a single GCSE (o levels at the time!) and went back to college at 24. Having a child really motivates you and i now have a degree and phd. (not that i use it SAHM again ). Im not entirely sure about the costs now, but i think you are entitled to the same grant as non mature students, i didn't have to pay my grant back but had a student loan. I am assuming it will be similar.
If i were you i would look into things you might like to do, have a look at what qualifications you might need to do it and if they are offered locally. The most common route for mature students is to do an access course, which covers the general areas covered by a level and study skills etc. If you are really unsure about what you might like to study you can do a pre access course to get your study skills up to speed again.
Depending on what you study, the contact hours and level of study it will be hard in terms of time. BUT i noticed that actually mature students with young families do as well, if not better than students who have some serious drinking and socialising to keep up with. You HAVE to be strict with yourself about deadlines etc and you make sure you utilise what time you do have. What you definately DO need is a supportive partner - especially to listen to you whinge when you are juggling deadlines. I found my university lecturers totally sympathetic to a parents needs, they get so sick of work not being done due to hang overs etc that when you go to them to extend deadlines they are more than happy to do so as they understand the family dynamic.
Absolutely the best thing i ever did going to university so pick a course and do it. You could even do a course part time, a friend of mine did a law degree this way, she had a handful of GCSEs, started part time law diploma and moved on to degree. I went the access course route into full time science degree - i think you have to self fund part time degrees though - expensive. There are funds available for students with financial pressures and parents are looked upon favourably.
There is LOADs out there, you just have to go and get it - have fun!