I'm having trouble imagining what you mean by the government stealing the person as a child or how the government would pose as someone's family. The basic details of what happened are needed to know what kind of legal issue this would be. It also matter in what state this occurred, how long ago it happened, how and when the person found out about it, and what provable damages the person suffered from it? What kind of "crimes against humanity" do you think occurred? Finally, which government agency took that action?
Most civil litigation cases have time limit in which the lawsuit compliant (which is what starts the lawsuit) must be filed. If the person misses that date, there is typically nothing that can be done after that date has passed. That time limit is known as the statut of limitations.
You haven't provided any facts as to what happened, so all I can recommend is that you start with an attorney who handles civil rights cases
