I only take kids till they start school so they start generally around 11-12 months and leave to start JK. That is a best case scenerio. Now if the parents are planning another baby around the time the first one is 18 months you are needing to plan for a potential mat leave with the mom not having any idea of her plans and sometimes it means them moving to a bigger house too so if location doesn't work any more then you have a space to fill.

I try to depend on the money from three kids and treat the income from the others as bonus money to be saved for lean times.