Telegraphic Speech

The omission of certain words and grammatical morphemes resembles what is typically seen in a brief telegram, hence the term telegraphic speech. Telegraphic speech is seen developmentally when a child moves beyond the two-word, relational stage of language development and begins to express longer, three-word sentences using a finite set of grammatical categories, such as nouns, verbs, and adjective. 

You can see these kind of  omission in this video