I'd definitely suggest being kind to yourself. Maybe do a "SWOT" analysis of your skills and your experience. You sound determined, resilient and realistic overall, plus your time management is obviously good if you're bringing up children. Are you sure you're getting all the benefits you're entitled to? And claiming what you can from HMRC against tax and allowances for your self-employed work?
It might be worth having a look at your local college to see if they have any funded courses for those whose annual income is under a certain amount. Our local college in Somerset offers this, and I know City College Plymouth offers these, for instance - www.cityplym.ac.uk/adult-education-funding/- there's also some useful information at www.moneysavingexpert.com/family/grants-education/#level2
There is very good advice on here about contacting your local college/university/hospital or NHS Trust and council to see if you can get yourself on their bank staff list. People outside the NHS tend only to associate it with doctors and nurses, but every hospital or Trust i like a village, and there is a whole range of work available. Have a look at NHS Jobs for some ideas; jobs are added every day and it's the UK's largest employer.
If teaching appeals, have a look at www.gov.uk/teacher-training-funding and getintoteaching.education.gov.uk/explore-my-options/become-an-early-years-teacher to see what funding might be available for you; you might need to do an access course first, but many local colleges offer these.
And does your local council or college maintain a register of part-time/sessional tutors at all? Though again, I know these vacancies have been decimated over the last ten years.
There's an online event about routes into teaching coming up on 13 January which is a) free and b) in the evening if you're interested - you do need to register though, I think - getintoteaching.education.gov.uk/teaching-events/online-events/introduction-to-teacher-training-options-1
And you've mentioned teaching swimming to, for instance, those with SEN; one idea might be www.swimtime.org/opportunities/become-a-swimming-teacher/ - though I couldn't quite work out from a brief look at the site if it's a franchise or if they employ teachers directly.
Open University courses do not come cheap these days, so that might not be an option for OP right now. Even studying at a bricks and mortar university is hideously expensive, and for many subjects the financial rug has been pulled out of vocational education long since.
Lots of people are suggesting writing; as someone who has been writing short-form non-fiction for around 25 years alongside the day job now and while it brings in a little money, it's certainly not enough for a full-time income; when I had to stop working outside the home for health reasons I had to find various other strings to my bow. And my qualifications and experience are wide-ranging; but I also live in the rural south west so finding those openings takes a lot of work and it has taken me about a year to build up to a reasonable annual income from several different sources and skillsets. And that has included looking at sites that some people turn their noses up at, like PeoplePerHour, UpWork and others.
The ALCS surveys show over the last couple of years that writers earn, on average, if they're lucky, around £6,000 pa from writing; some of them supplement it by teaching workshops and the like, but unless you're JK Rowling or MC Beaton, or very, very lucky, it's very hard to earn a full time living from writing alone these days. There are some subject areas where the pay is relatively good (blockchain at the moment, for instance) but you usually need really specialist knowledge.
@PlanDeRaccordement, out of curiosity, where are you finding these copywriter/copyeditor openings where the pay is really good? Can you share any sites or sources? In some areas, £15 an hour is a decent rate for the general administration work I mainly do; while I do know of someone in London who also writes on various topics but also (claims she) earns £270 an hour for "love counselling". At least, that's what she says she charges...
I am smiling a bit at some of the comments from people who can only live in Yummymummy world, Kensington-on-Coquet or St-John's-Wood-on-Exe - things that might work in well-heeled parts of London, like delivering mindfulness sessions to bored and wealthy stay-at-home-mums with high-earning husbands. I'm not sure how well that approach would work in poorer parts of the country where the only time such wealthy folk are seen is when they've visiting their second homes on summer recess 
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OP, good luck with the mentoring and everything else. If you want to drop me a PM for ideas of further websites or information sources to look into you're very welcome.