I found an interesting list of speech development milestones at the National Institute of Deafness and other Communication Disorders. If you scroll down, there is a section that approximates a child’s speech development based on age.

This is important because the sooner any speech or language problems are discovered, the easier it is for the child to get on with their education without losing interest in learning or losing confidence. Sometimes, problems can simply be resolved by training underdeveloped muscles in the mouth.