I have only heard of the rule through word of mouth ,however I currently care for 2 1 year olds another who will be 2 in June and 1 that will be 3 in may as well as another 1 year old starting next month.I have a friend with 2 year old twins that usually comes once a week for a playdate ,these rules are dumb and made by people sitting in a office chair looking to make rules.I would like these rule makers to take a walk in any of our shoes then see what they think of their rule.As for me i will continue to have my friend over !!