Believe you are mistaken in the birth date.... the 1900 census shows July 1877.
WWI Draft Registration:9/7/1918, Springfield City MO Howard Wesley Mann, 42yo, b.7/12/1878 Residence:1405 E. Walnut, Springfield MO Occupation:Self-employed general contractor Address:Springfield MO Headquarters Nearest Relative:Anna J. Mann (same residence) Tall, Slender, Dk.Grey Eyes, Dk.Brown Hair
California Death Index: Howard W. Mann b.7/12/1877 Michigan, d.3/8/1947 Los Angeles County, S/S#546-14-8798 Anna Jual Mann b.3/12/1885 Missouri, d.12/19/1944 Los Angeles County, Father's surname Smith, Mother's maiden name Wright
The 1920 census shows children Guy 15yo, Lester 10yo, and Mary M. 9/12mo.
Possible.... California Death Index: Guy Howard Mann b.9/30/1904 Missouri, d.2/12/1982 Los Angeles County, Mother's maiden name Smith Lester Demont Mann b.12/20/1910 Missouri, d.5/5/1982 Los Angeles County. Mary Margaret Costello & Niswander b.4/3/1919 Missouri, d.1/14/1949 San Bernardino County, Father's surname Mann, Mother's maiden name Smith.