Mary Poppins will literally be returning onto the scene so many years later and will meet the now-grown versions of Michael (Ben Whishaw) and Jane, as well as their children, who will be influenced by the famous Ms. Poppins and the street lamplighter, Jack.
Lin-Manuel Miranda also previously said the writers of the new movie took stuff from some of the eight Mary Poppins books by P.L. Travers to fit into the new movie with the grown-up versions of Michael and Jane.
From what we know about Mary Poppins Returns, the movie will be set during the 1930s, in Depression Era London.