Duress

Are you in the US?
Did you terminate all your parental rights, or are the children just in custody of the state, perhaps in a foster home now.

There sould be social workers who would work with you. The court would have certain conditions that you would have to meet to get the children back.

Probably depends on why the pregnant mother was speaking to an attorney in the first place. If she were arrested and later exonerated, I would think a duress argument would be pretty valid. If she were lawfully under arrest, I would tend to doubt it.

But that doesn't mean she couldn't get her children back. Most jurisdictions give more than just lip-service to attempting to look out for the best interest of children... and separating children from parents and/or keeping them separate is, generally speaking, a last resort. Said mother should consult a local attorney immediately, because the longer she waits the harder it will likely be.