I think the main issue I have is that I don't think 4 days as a teacher is really part time! I will still do the majority of the work (and get paid the majority) but I see the person who does my 1 day will do just that, teach for 5 hours and I'll do all the admin, planning, parent interviews etc.
But anyway...
I'm about to go on ML to have dc2. I worked full time after my first baby, it was tough some days but have a v supportive dh so it definitely was manageable.
Dh and I agreed that after dc 2 I would go 4 days a week as childminder is going 4 days and we don't want to be reliant on family. The plan is that our dc will be in paid Childcare for 2 days a week, I'll do one day.
Now for the BU bit. I feel I am. My dh does shift work and he is at home various different days during the week, sometimes 1 or sometimes as many as 3 during the week. On these days he does all the Childcare obviously. He's not great at multitasking so doesn't do cleaning or ironing etc when he's at home- he spends the day with ds, out and about, walks, park, toddler groups. He will always have dinner cooked when I get home but I will have to tell him what to cook, I don't mind this as left to his own devices will produce some strange concoctions! 
Anyway, everybody I know who is a teacher does 2/3 days when they have children and I struggling so hard not to be petulant that I can't do this. It wouldn't make sense to have the two of us, dh and me, at home during the week so it does make sense I suppose.
I am the higher earner so financially it wouldn't make sense for me to drop more days at work.
My mum does one day of Childcare for us and mil does 1-2 days a month, so this arrangement will continue.
I guess I feel guilty for not being part time, in my mind part time is not 4 days. I do get comments from people about working and I have had to justify myself for not being part time, it's really no one else's business but I find it hard not to be defensive. Sorry if I'm rambling.
AIBVVVU?