To throw down the gauntlet means to issue a challenge or invitation, and in this context Lestat is issuing a challenge to the pampered children.
Consider the staetement "No wonder Lestat had chosen this place to offer a challenge or invitation for an argument or competition, in the main, these pampered children were good.". Based on this statement, is "No wonder Lestat had chosen this place to throw down the gauntlet, in the main, these pampered children were good." a true statement? Yes/no/unknown