This verse uses a number of phrases associated Jesus. Christ often uses the phrase "children of the kingdom," but he usually uses it to refer to the "kingdom of the sky." Here it seems to refer to the children of Israel. This is atypical. The phrase usually means the "good seed" (Matthew 13:38).

This is the first time the phrase "outer darkness." It is used elsewhere in parables (Matthew 22:13, Matthew 25:30). However, it is not in the form of an adjective and a noun, but of two adjectives used as nouns, "the darkness" followed by "the outer." 

The word translated as "gnashing" means "biting" or chattering," not "grinding," which is the meaning of "gnashing." The weeping and chattering teeth phrase seems humorous in nature. Jesus speaks parable verses that use this phrase.  It is always used at the end of the verse as a punchline. "The weeping and gnashing of teeth" are not the common participle forms. They are a more unusual form that we might translate into English as "lamentation" and "mastication." The words are theatrical so they seem more like Jesus's humor than anger.  For more on this topic, see this article.