According to Article 20 of the Federal Law from 15 .08 .1996 N 114-FZ "On the procedure for leaving the Russian Federation and entry into the Russian Federation": "A minor citizen of the Russian Federation, as a rule, leaves the Russian Federation jointly with at least one of the parents, adoptive parents, guardians or trustees..In the event that an underage citizen of the Russian Federation leaves the Russian Federation unaccompanied, he must carry along with him / her a notarially registered consent of the named persons for the departure of a minor citizen of the Russian Federation, specifying the time of departure and the state (states) that he intends to visit ... "

That is, consent is required only if the child travels without parents. If one of the parents is traveling with a minor, the main thing is to confirm the relationship. To do this, enough information in your passport, if the child is inscribed to you in the document, or a birth certificate, indicating who is who to whom. - $

This refers to leaving the territory of the Russian Federation.