This is a very interesting thread, thanks everyone for your thoughtful contributions.
The flexibility thing is double-edged, I think. Yes, academia can be very forgiving, especially out of term. But it's trickier when it comes to cancelling classes to stay home - it's not like someone else can just cover you (not at my institution anyway), and rescheduling isn't always an option either. I've only had to do it a couple of times, and I have a generally supportive department head, but it still causes a bit of hassle. So in that respect, a less flexible job sometimes might be preferable - just take the day off, someone else covers, you don't have to 'make up the time' in the evenings or at weekends.
Since going back after my second, I've definitely lost the love - LisaSimpsonsBFF, your post really resonated with me. I really don't want to work evenings and weekends. I've considered trying to get into academic administration, but it's hard to break into here. Plus, a 9-5 with a commute would be more like a 8-6, and that's tricky with childcare. At the moment, so we can manage drop off and pick up between us, I'm doing 7.30-3, some evenings, and usually a half day at the weekend. So, I have to make it work for the moment anyway, and there is where the flexibility of academic definitely helps. But I'm exhausted, and I'm not giving my best in the classroom or at home.
In order to be properly successful though, I think you need to have a relatively light teaching load and be very organised, and probably work weekends. I do know a few very successful female academics with more than one kid, but crucially, these women are all 10-20 years older than me (I'm 40). They all acknowledge it was easier to be successful when they had young kids, as the environment wasn't as pressured. Now with the REF, and the obsession with big grants, outreach etc, it's much harder.