Questions

I just don't understand families sometimes. 

Jack, Mildred, and Margaret (the latter two twins) were born in California in the 1920s.  By the 1930s their parents divorced.

Jack is found in Michigan in 1930 with his father and his father's new wife.  In 1940 he is in New Jersey with his father and step-mother.

Mildred is the same as Jack except that she is living with a different family at the age of 6 in Michigan.

Margaret is the same as Jack.

Mama can't be located on the 1920 or later censuses.  It's possible she remarried or that she was deceased after the twins were born.   There is one possibility for her on the 1930 census which has her back in Iowa and with a son born before she married Jack, Mildred and Margaret's father.  That possibility has been proven not to be her. Where is mama?

I am amazed at the traveling the family did when it wasn't quick to get anywhere. Why were the kids living with their father instead of their mother?  Why is Mildred with a different family in 1930?