Nursery fees are ridiculous, as is trying to chop and change days, simply not possible. It means as a household, we are worse off once my mrs goes back to work.
It was the same situation for my wife, but we made the decision to keep her in the workforce for those years as she works in tech and in 5 years (two kids) her skills risked becoming irrelevant if she stays out of it for that long. So she reduced her hours instead, but even that way it took several years after she went back full time to be at the right "place" for her career / skillset.