Times between children

What seems to be the average amount of time it takes (in-game) for a couple in VF & VF2 to have subsequent children after the first one? In my VF games the soonest my couples will have another child is 4 yrs. Anybody else's couples able to have them sooner - maybe have to wait longer?

Make sure they're fed and all that, if they are tired etc they are less likely to have a kid

Pretty sure it works on a 2-year gap, with the second child running around after the first child turns 4. I keep all of my LDoW games running on the fastest options btw