No. Disney+ is not only for children, even though family viewing is a major part of its identity. Marvel, Star Wars, documentaries, legacy films, and wider franchise fandom all broaden the service well beyond a children-only pitch.
The reason this misconception survives is that Disney+ does have a clear centre of gravity. Its strongest case is still families, Disney-heavy households, and viewers who know that Marvel, Star Wars, Pixar, or classic Disney content will get regular use, which is why people reduce it to a narrower stereotype than it really deserves.