For me I like aboaut 15 months to 2 years. They are usually walking and with that finding so many new things in the day that excite them and then for the next year you can expand on that curiosity. Before that it is all just mechanical care in the sense of physical needs - diapers, food, sleep and in between you attempt to do other things but your attention becomes more on the others in care in since the babies have their personal time spent on the care needs. After age 2 you are more at the mercy of what the parents are doing at home and then heaven forbid a child goes to school. I don't even take JK/SK any more because I couldn't stand the attitude - and they moved the bus stop from the end of my driveway.