Nobody seems to have asked the op WHY she wants to do this? Maybe she really loves the law and wants to practice? I don't think she should be put off doing it if she is really interested, but she needs to understand that with kids under 10, it's going to be a rough ride.
I'm a finance lawyer and I work in the magic circle. I am lucky to have a husband who works much more flexible hours at his big 4 accountancy firm so we manage the kids and our family lives etc better than many.
Even now, I find that 100 hour weeks exist - regularly and even in areas considered "nicer" or "less stressful" like pensions, employment and real estate. Clients want more work for less money so everyone is constantly under pressure to prove themselves. Not least of which, the juniors and trainees.
Trainees are expected to try to impress as an absolute basic requirement - there are 90 trainees in an intake here and only around 60-70 jobs a year. All of them come from good academic backgrounds and work hard, so we are constantly looking for any way to work out who we want for the permanent jobs. It's ruthless, and it means that they work longer and longer hours to impress.
I'm going to get flamed for this but... If my trainee told me she had to leave before about 7pm to pick up her kids, spend time with them etc etc I would respect it and I wouldn't stop her doing so (I'm a nice supervisor) but she would have to be absolutely amazing academically, the most efficient person I had ever met and an all round superstar for me to recommend her for a qualification job over a younger person who was good at the job, efficient, worked long hours whenever required, produced more work and could give more to the role. I have to consider the firm when I give my recommendations, not just each person. It's ruthless here.
I have friends in smaller firms up North. They practice in areas like property, employment, and dispute resolution. They don't work 100 hour weeks, but they do stay in the office regularly until 7pm and they are expected to drop everything on a weekend if a massive piece of work that the firm can profit from comes up. They have less job stability than me because their firms are smaller, which means that they constantly have to compete in the way that our trainees do and they don't earn amazing money (it's good, but no better than a civil service role). It's different but equally as ruthless and stressful.
To change industry at your age you need to be certain that you can commit. if you love the law and want to practice it that badly, just do it and be aware of the commitment required from you. But if you're basing your decision on what you've seen on TV and heard from people about the wages, don't do it - it's not worth it.