Imprisoned mothers would work, too.
Here's the suggestion I made via LC's suggested terminology form:
"I recommend adding terminology to complement this existing heading, http://id.loc.gov/authorities/sh85023573#concept 'Children of women prisoners': Incarcerated mothers.
"The immediate warrant is a zine called 'For my sisters and the burden we share,' published by the Kids-A-Part Program. I can send you a pdf of the zine if you like."
[mostly their language]
It's weird that there's a heading for the children, but not the mothers, right?