MatildasMummy, I work from home too, for a big City law firm, so maybe a similar company in terms of outlook, i.e. expecting me to be on the end of the phone when they need me on my working days etc. tbh, I think that it's reasonable that they should be able to expect me to be here for them between 9 and 5 on my working days. Outside of those days, I don't answer the phone, or look at email, and it works fine.
I really do think trying to work from home with DD there is a bit crazy, sorry. I do 2 days a week, and both my DSs are in nursery for those 2 days. While I was on mat leave (at exactly the same time as you!), I did a half day a week from dec to march, while DS1 was in nursery, and DS2 was asleep, and I found even that hard to manage. I know this isn't what you want to hear, but I can see how your boss is worried that you won't be able to perform your role properly with DD at home (esp as she gets older ). My DS2 was also born in September and I would find it impossible to work with him here.
I think that trying to juggle everything will mean that you are stressed, your DD will be stressed, and your boss will be stressed. Can you get auntie and grandma to have DD for the time you are working between now and July?
Although agree it was naughty of him to give only 24 hours notice when you'd agreed a week.