Families of Prisoners Support Group
This community is dedicated to families that have been disrupted by prison. Having a loved one incarcerated or having been incarcerated comes with its own unique challenges that require support and understanding. Join the group to find others who know what you're going through, and to seek advice or share your experience.

If it were me, I'd tell her the very truth...casually .... from the beginning but only if she asks and "downplay" it. Don't give details but say we ran into some bad luck in our lives but we're trying to make things right.
People don't need to know your business. It has nothing to do with shame but it has to do with privacy and boundaries.
If she does judge then that's one person you don't need in your life, right?
If you want to be more upfront about it, I would wait until she asked about your husband. Just say he is in prison right now. And leave it at that. If she asks more questions about it, let her know respectfully you don't want to discuss it with the kids around. Like Ms.901996C said, it's about privacy and boundaries.
Now that my daughters are getting older, they are wanting to play with kids from their schools and like you, I'm nervous about the dreaded husband questions. But, we'll get through it and possibly make some new mom friends in the future :)