1900 United States Federal Census
Name: Edward A Mosby
Home in 1900: Brookland, Henrico, Virginia
Age: 9.12
Estimated Birth Year: abt 1899
Birthplace: Virginia
Relationship to head-of-house: Grandson
Race: White
Household Members: Name Age
James Tinesley 64
Lenora C Tinesley 44
Cora L Tinesley 11
Edward L Mosby 24
Arminta L Mosby 20
Edward A Mosby 9.12
Florence Mosby 20
Mannie Mosby 18
Percy Willis 12

I find no Edward Arnold Mosby but do find:

Mosby, E. C.
Confederate
Infantry
9th Regiment, Texas Infantry (Maxey's) (Young's)

Mosby, E. C.
Confederate
Infantry
Gould's Company, Texas State Troops (Clarksville Light Infantry)

Mosby, E.M.
Confederate
Infantry
35th Regiment, Arkansas Infantry

Mosby, Ennis
Union
Artillery
12th Regiment, United States Colored Heavy Artillery

JR