I switch careers in my 30s to teaching.
I think it is difficult to know whether you love teaching until you try it, but you certainly have to be passionate about it in order to get onto a PGCE course and get your first job.
Going back to university was a bit of a culture shock to me. The PGCE was pretty easy when coming from a high-pressure blue-chip environment, but it is best to keep quiet about these kind of opinions.
As a lawyer, you will already possess most of the transferrable skills (eg time-management, dealing with paperwork, stress management, presentation skills) that you need to be a successful teacher. The unknown is what you will be like in a class of children.
I gave up teaching after a year and a half (had another child and decided to SAH) because, if truth be told, I didn't enjoy it. I didn't enjoy the unknowns that came with the job - what mood would specific difficult pupils be in that day and would this wreck my lesson and impact on the learning of others, etc. A lot of teachers thrive on this, though. I didn't regret leaving my old job and trying out teaching, even though I became a quitter. I simply moved onto a new part of my life which I loved at the time. If I stayed at my old job, I wouldn't have had any more children, and certainly not the ones I have now (which is hard to think about).
I returned to teaching many years later and now love my job. I'm only just earning more than my previous job which I left almost 20 years ago.
When you leave a lucrative job to become a teacher, you are not doing it for the money. It is a career that gives you time off with your children in the holidays, is something you can come back to after a career break, and offers promotion opportunities if you want it.