Updated: Nov 19, 2019
Apparently, there is some sort of debate going on in the fascinating world of speech-language pathology that says the above are "new" milestones for speech sound development. But, in reality, these have pretty much been the measure, backed by a ton of research, for as long as it's been published. These are "the" norms folks. Your kiddos should pretty much speak like an adult by the time they are six years old. And if by seven or eight, they aren't, it's time for intervention!