Elledubloo, what stage of training are you at?
I don't know much about lawyers, but as far as doctors go, I am a core medical trainee with an 18 month old and another on the way. I had a year off for maternity leave and then went back part time. If you are in a training post, I believe they have to try and offer you less than full time working if you ask for it. I am not sure if this is the case for all training programmes but I think so. The BMA were VERY helpful outlining all this, and you can talk to them before you are willing to talk to work, early on in the pregnancy for example.
So I work a job share with another SHO. I still obviously do nights, weekends, etc. My DP has switched to 3 days per week, luckily his work can be flexible which days these are as long as they know in advance, so he works around my shifts. On night shifts or weekends or during busy patches my mum usually comes to stay, for an extra pair of hands. If she lived closer, she would probably take DD one day a week, but even as is she's up here every 2 weeks for a couple of days. We also do 1-2 days a week in nursery. So it's a bit of a mix of me, DP, nursery and my mum doing the childcare. Works for us.
Me and DP both wanted to be involved in rearing our kids and so these are the financial and career sacrifices we've made. Though I am obviously doing core medical training at half the speed, it has its advantages too - lovely work life balance, less exam pressure!, I actually get a wider range experience as I'll do 12 jobs in CMT rather than the standard 6. I understand the pressures junior docs, particularly mums are under, and I hope this will make me a better supervisor when I get to that point. Most doctors I know are not part time - our culture is not very accepting of it. As I said though, most training programmes have to try and accommodate it if you ask.
I could not have left my baby at 6 months - I was still breastfeeding every couple of hours at that point - and when you are up all night with the baby etc, work IS harder - I am pretty shattered even working part time. (and as I'm sure you're aware, part time as a junior doc is often 40 hours a week anyway - I did 56 the other week!) You may feel a bit differently once you are with your baby.
These threads are always full of men who "can't" possibly work any less or help out, even though women with equally demanding jobs DO work less and DO all the bloody childcare - it isn't "can't", it's "won't" - it would be good to have these discussions up front before the baby is here and you are both shattered and resentful! Female lawyers work flexibly and take time off - parental leave now exists - it doesn't have to all be on you.
Just some food for thought! Hope it's helpful.
As others above have said, I think your MIL will offer if she wants to do the childcare, and she will offer the amount she is happy to do.