Historically for decennial and American Community Survey data, the Census Bureau has estimates for households in which the householder has both a spouse and at least one stepchild present. You can find data on stepchildren on data.census.gov (e.g. Table B09018).
Note that step relationships that exist across households are not captured in decennial, American Community Survey, Current Population Survey or the Survey of Income and Program Participation data since data are collected based on the address being in the sample.