I didn't answer earlier because my experience isn't very recent. However, since no-one's replied yet, here goes.
You don't say how old you are, but you may wish to make a start by volunteering your help somewhere - maybe in a youth club, school, outdoor centre etc etc. It can often be the way into part-time employment, first as an assistant leader and then as a leader, perhaps with some specialism (I did special needs - learning and physically disabled). It goes without saying that you will need to agree to a CRB check, so a clean record in the appropriate areas is a must.
There is a degree-level qualification in youth and community work. I think there's a two-year diploma course, with the option of another year to top up to a degree. The course usually involves theoretical and practical work, including several placements. I guess universities insist on minimum qualifications for these courses, but a lot of mature applicants get in by dint of their experience.
If you're looking at pre-degree subjects in order to do this, then you might consider sociology, psychology, health and social care, plus the usual stuff like maths, english etc. There again, if you can offer artistic, musical or performance skills, you'd be quite valuable to a youth work team.
Outdoor skills (canoeing, climbing, etc etc) are also useful, as is a driving licence.
Hope this helps.