Most people I know have decided not to have kids or have only one, and yes, a lot of it has to do with feeling like they don't have enough time or energy. Economic concerns are another reason.

I am married.My husband and I don't have children by choice. I work from home, so I have more time than those that have to commute. Still I don't know how I could do it.

The few people I know with more children seem to either have significant family support, money to hire a lot of help, or both.

The sabbatical idea sounds good. Although, like you say, corporations would never go for it!