Given how young Millie is, and the relatively little time the two have been together, it would be a little strange if they were already engaged. Their bond seems to be pretty strong, though, and being a star at such a young age can lead you to become more mature more quickly. Millie has certainly been famous for quite some time, and she may feel that she’s ready to enter the adult world even though she’s still quite young.

Source: https://www.distractify.com/p/millie-bobby-brown-engaged