I looked it up, the stat is 43% of mothers leave the work force after having a baby. Yeah, 90% is an exaggeration, but 43% is a huge chunk of women. This isn't intended to debate you, just to put a real number on it. The article I got this stat from talks about some of the things you mentioned.

I'm far from an expert so I could be totally wrong but the little bit of literature I've read on outcomes for children suggests a full time stay at home parent provides the best outcomes. That almost certainly doesn't have to be the mom specifically, but if we're going to subsidize behavior, I would prefer to subsidize whatever behavior provides the best outcomes for children. The article below suggests part time work from home opportunities with deadline based projects. That might be a reasonable answer, but again someone with actual expertise on child rearing/psychology should set policy here. The best outcomes might not be [parent] getting back to work in 6 months or even a year.

https://www.theatlantic.com/sexes/archive/2013/04/why-43-of-...