Yes, if they were born here, they are American citizens.
Some of the Russian agents were naturalized U.S. citizens and were stripped of their citizenship prior to being shipped back to Russia. Ostensibly because they never registered as foreign agents of Russia.
My point is that they never were legally recognized to be in the country in the first place - therefore, there should be no jurisdiction as pertains to the privilege of their children being born U.S. citizens.
And the same would go to all illegal aliens [which the Russians were]. Registration with the government is a requirement to be in the U.S. and to enjoy its benefits ...