How can you take away their parental rights? There's no law that says American children must be raised in the US.
You deport the parents and let them decide where their children should be raised. They could raise them in Mexico, or arrange for them to be raised by an American relative, for example.
In the mean time, they apply for US citizenship through normal channels.
1. Leave and take any minor children with them.
2. Leave and make verifiable arrangements to leave their Anchor Babies with a US citizen guardian that will provide for them until age 18.
3. Anchor Babies become wards of the state and can be emancipated after age 16 if they can prove they are self supporting.