So many questions!
Who are the three children shown in this vintage real photo postcard?
Where was this picture taken?
What were there lives like?
What happened to them when they grew up?
According to playle.com, a website that deals with vintage postcards, stamps and more: "Most Real Photo Postcards, abbreviated RPPC, have information on their backs to help in identifying the manufacturer of the photographic paper that was used by the postcard publisher. If you can identify the paper manufacturer, you can approximate the age of the old postcard."
In this case, the stamp box contains the word AZO and, importantly, four triangles in the corner that are pointed upward.
According to this page on playle.com, those four upward triangles date the postcard to between 1904 and 1918. About a century ago.
AZO photographic paper was produced by Kodak until 2005 or 2006.
So, we have a time period. But little else. Wouldn't it be wonderful to know who these people were?