The movie's final scene suggests that the monster will always be around, but Amelia will learn how to deal with it and still live the life that she wants to live. The Babdook monster represents grief itself, which is a clever and moving metaphor.
He has a seizure in one scene, and seizure disorders are often comorbid with autism spectrum disorders, particularly in children. But The Babadook never says autism, or neurodivergent, or neurological disorder. Because the movie is not interested in Samuel, it is not interested in diagnosis or intervention for him.