I was once told by a recruitment agent (when I expressed a desire to get out of the law) that they often place ex-solicitors in marketing positions. Apparently the skills learned in law firms transfer quite well to marketing... And I think marketing positions (at least in law firms) still pay relatively well.
What about re-training as a barrister? You would still have to put in the hours and there is the pressure that goes with being self-employed, of course, but at least you'd have a bit more flexibility about when and where you work (eg getting home at a reasonable hour to see the dcs and then working in the evenings after the dcs have gone to bed).
Or a Professional Support Lawyer? Although a friend who worked as a PSL told me that she often got phoned/emailed after 5.30 by the fee earners who would spend the work day doing billable hours and then following up with her on the non-billable stuff after hours. I guess the same is probably true of marketing roles in law firms. On the plus side, though, it's often possible to go part time or job share PSL roles.
Also keep an eye on the GLS vacancies website. Though they don't pay as well as law firms. Friends of mine who used to work at the GLS seemed to get a lot of flexibility about PT or job share options and working from home where required.
In-house/GLS/PSL jobs often sell themselves on the basis of their work/life balance. Where I work (in-house) there are lots of ex-solicitors/barristers and everyone (including those in senior positions) is quite open about the fact that they moved in-house in order to leave the office on time in the evenings.
I took a pay cut when I moved but I probably earn the same per hour as I did when I worked in a law firm, considering that I am not expected to start before 9.30am and am expected to leave at 5.30pm sharp (emergencies excepted, of course) and no weekends.
I am so much happier since I moved in-house - great quality of work, reasonable hours and colleagues with real people management skills!