number of kids
had more than 2 kids
first two births boys
first two births girls
first birth boy
second birth boy
first two kids are of same sex
=1 if 2nd birth is twin
age of mom
age of mom at first birth
=1 of black
=1 if hispanic
mom worked last year
weeks worked mom
hours of work per week, mom
mom's labor income, $1000s
family income, $1000s
'non-mom' income, $1000s
mom's years of education