Speech is the verbal expression of language which includes articulation- (the way that sounds and words are formed), fluency and prosody (the rhythm, intonation, stress, and related attributes of speech) and voice.
Language is the foundational system of giving and receiving information in a meaningful way. It is understanding and being understood in communication. Language includes five areas: phonology (sound structure), morphology (word structure), syntax (sentence structure and grammar), semantics (vocabulary), and pragmatics (social language).
Speech and language therapy helps children speak clearly and communicate effectively, as well as understand communication and process language.
Additional information about speech and language developmental milestones at:
https://www.asha.org/public/speech/development/chart/
https://www.asha.org/public/developmental-milestones/