A post accompanying a YouTube video of the performance says the 90-year-old Van Dyke and the other three members of his quartet, The Vantastix, had just finished an appearance on a local television show before going out for breakfast.
The video shows the quartet seated with pancakes at the table and singing the theme song to the 1968 British musical, which starred Van Dyke.
VIDEO: Dick Van Dyke performs 'Mary Poppins' tune at Walt Disney's birthplace
Breakfast at Denny's, with a side of grits makes me want to sing!! https://t.co/raoDGZSCV5— Dick Van Dyke (@iammrvandy) August 13, 2016
Van Dyke and The Vantastix are promoting a show later this month in southern California.
VIDEO: Flash mob performs 'Mary Poppins' medley for Dick Van Dyke's 90th birthday