The American Heritage Dictionary offers the following definition:
sen·tence (sěn’təns) n.
- A grammatical unit that is syntactically independent and has a subject that is expressed or, as in imperative sentences, understood and a predicate that contains at least one finite verb.
I, therefore, present to the world Peter’s first self-assembled sentence, uttered repeatedly until the request was honored:
“I want juice.”
It seems to meet the defined criteria. It’s blunt, not terribly polite, but delightful to hear!