The Adaptive Child is one of the “roles” recognized in Transactional Analysis, a communication theory developed by psychiatrist Eric Berne. The adaptive child behaves poorly in an effort to get what they want. Their behavior is adaptive in that it is not what a parent would want, but for the child it works because it gets them the desired outcome.
An example would be a child who whines (and whines and whines) to get what they want. The adaptive child has learned that if they whine long enough they will get rewarded. Whining is not a desirable behavior but it gets rewarded so the child has adapted it as a way to get their needs met.