Parents
John William Klein 1865–1940
Mabel Emma Parker-Klein 1873–1945
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Illinois, U.S., County Marriage Records, 1800-1940
Name: Frank William Klein
Gender: Male
Age: 18
Birth Year: abt 1891
Marriage Date: 14 Jun 1909
Marriage Place: Winnebago, Illinois, USA
Father: John W Klein
Mother: Klein
Spouse: Mabel V Alberts
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1910 United States Federal Census
Name: Frank Klein
Age in 1910: 24
Birth Date: 1886
Birthplace: Illinois
Home in 1910: Rockford Ward 4, Winnebago, Illinois, USA
Street: North Horseman St
Race: White
Gender: Male
Relation to Head of House: Lodger
Marital Status: Married
Father's Birthplace: Illinois
Mother's Birthplace: Illinois
Native Tongue: English
Occupation: Leather Worker
Industry: Tannery
Employer, Employee or Other: Wage Earner
Able to read: Yes
Able to Write: Yes
Years Married: 1
Out of Work: Y
Number of Weeks Out of Work: 0
Household Members Age Relationship
William Rutsch 56 Head
Jennie Rutsch 52 Wife
George Rutsch 22 Son
Cora Rutsch 24 Daughter
Frank Klein 24 Lodger
Mabel Klein 20 Lodger
Fred Simon 38 Brother-in-law
Ernest Simon 15 Nephew
Hazel Simon 13 Niece
Hellen Simon 10 Niece
Albert Simon 8 Nephew
Harold Simon 6 Nephew
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I was unable to locate Frank in 1920 or later.
Either he and Mabel separated or he died?
Further, Mabel remarried:
Indiana, U.S., Marriage Index, 1800-1941
Name: Mabel Alberts
Spouse Name: Guy S. Mutimer
Marriage Date: 6 Dec 1919
Marriage County: Lake
ALSO, both daughters were living with "foster parents":

1920 United States Federal Census
Name: Helen Walters
Age: 8
Birth Year: abt 1912
Birthplace: Illinois
Home in 1920: Macomb Ward 2, McDonough, Illinois
Street: North White Street
Residence Date: 1920
Race: White
Gender: Female
Relation to Head of House: Niece
Marital Status: Single
Father's Birthplace: Illinois
Mother's Birthplace: Illinois
Attended School: yes
Household Members Age Relationship
Floyd Walters 29 Head
Blanch Walters 36 Sister
Helen Walters 8 Niece
Doris Bass 3 Niece
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1920 United States Federal Census
Name: Esther Lillian Kline
Age: 9
Birth Year: abt 1911
Birthplace: Illinois
Home in 1920: Union, Shelby, Iowa
Residence Date: 1920
Race: White
Gender: Female
Relation to Head of House: Foster Daughter
Marital Status: Single
Father's Birthplace: USA
Mother's Birthplace: Illinois
Able to Speak English: Yes
Attended School: yes
Able to read: Yes
Able to Write: Yes
Household Members Age Relationship
Henry B North 44 Head
Minnie A North 44 Wife
William H North 66 Father
Ralph C North 14 Son
Esther Lillian Kline 9 Foster Daughter
John North 36 Brother
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https://www.findagrave.com/memorial/44879912/helen-bernice-walters
Helen Bernice Klein Walters
BIRTH 18 Oct 1912
Illinois, USA
DEATH 7 Sep 1997 (aged 84)
Kern County, California, USA
BURIAL
Mountain View Memorial Park
Barstow, San Bernardino County, California, USA
PLOT 16 18 4
MEMORIAL ID 44879912
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https://www.findagrave.com/memorial/15339805/esther-lillian-rosenow
Esther Lillian Klein Rosenow
BIRTH 18 May 1910
Rockford, Winnebago County, Illinois, USA
DEATH 21 Nov 1981 (aged 71)
Woodland, Yolo County, California, USA
BURIAL
Union Township Cemetery
Defiance, Shelby County, Iowa, USA
MEMORIAL ID 15339805