An Ancestry.com tree says Mabel Viola Johnson was called "Viola." That's common with Scandinavians - to be called by a middle name. We often see the first name in a record, and then later the "calling name," or see the first and middle name flipped. None of which proves that 1910 census is your family - but it probably is.
Since Charles immigrated so young, seems he would have been accompanied by an adult. Is that part of the family story about him?
A candidate in 1880?
1880 US Census
Alexandria, Douglas, Minnesota
Andrew Johnson 45 b abt 1835 Sweden
Anne S. Johnson 47 b abt 1833 Sweden
John Johnson 14 b abt 1866 Sweden
Mary Johnson 12 b abt 1868 Sweden
Charles Johnson 11 son, born about 1869 in Sweden <-----
Oscar Johnson 5 b abt 1875 Minnesota
(to clarify - I didn't look at the Ancestry tree I mentioned above)