How are cops supposed to know if they outgrew their seat? It also means that when they move to forward facing or a booster seat depends on the car seat you bought, not their height, (only their) age, or weight.
For older kids, here's the new rule: "A child at least 9 years old or has outgrown their booster seat AND the child can pass the "5 step test" may be restrained by a regular seatbelt, but they must be in a the back seat if possible under 13."
That's not too bad because they at least have a set age, but you still can't expect a parent to have a set of 4 booster seats ready to go to haul your kids friend's around.
Sucks, as this isn't as easy as saying it will be your responsibility and fault if the kid is injured. Odds are high this will just make a bad situation worse.