In the USA there's a definite "kid gap" around 4k-1st grade - before that, childcare if used is "open late" and flexible (if you have the cash) - and after 1st the kid is often mature enough to do simple movements on their own if school doesn't go long enough (walk to the library, or get into extra curricular activities, etc).

At 4k-1st you often have shortened hours, so if you're a working parent you need to arrange for transportation or be able to take long lunches, etc to move children from one place to another.

This "gap of annoyance" happens right about when you'd naturally be looking at a second or third kid as a possibility - I wonder how much effect it has on people.