I work 3 days, have done for 6 months now.
It's going really well, much better than I thought, but there's factors that have really helped:
My new division at work is hugely understaffed (8 vacancies, and 14FTEs, 20 of us, in post). So they're desperate for anyone good to stay. No-one else remotely fitting the spec applied for my post in the last year. And over 1/2 of us are part-time doing work for the division, even though some are full-time workers but work in other divisions or agencies some of the time.
Lots of people do some homeworking or work at other offices or on the move some of the time. So flexible working for whatever reason really works. My manager has a baby younger than mine, too.
I actually go into the office more than many people rather than home-working because I see people, have a rest on the train, and can write letters and make phone calls that are hard from home. And I can split myself into Home and Work mode and not really think about the other when I'm not there. So I don't have a pic of ds on my desk, for example.
Excellent nursery next to the station I commute from, and ds loves it. It was closed for one snow day but MrNC was working from home and I couldn't get to work, so worked out OK. Ds has been poorly a few times but only two days too sick to go in, one was a non-work day for me, one MrNC worked from home and we got various unemployed friends locally to cuddle ds when MrNC had to be on the phone.
I've got a lot better at planning time at work and just saying 'no' to stuff if I won't have time - but as everyone is overworked, we all have to do it so me being part-time doesn't make a difference. I did agree to two meetings on my off-days but only because they were round the corner from my parents and they could see ds.
Suspect helps that I actually have some cash left over after childcare+commute, and am really enjoying work (mostly). If I had more kids I'd be spending a lot more and would only do it if I were still enjoying the job. Or if ds was in school by then and costing less. Or would holiday+afterschool care plus all the other stuff older kids need cost as much as current nursery?