In accordance with Russian law (FZ of August 15, 1996 .N 114-FZ "On the procedure for leaving the Russian Federation and entry into the Russian Federation") for the departure of a minor child outside the Russian Federation, accompanied by one of the parents, the consent of the second is not required..However, from July 22, 2005 .by order of the Border Guard Service of the Federal Security Service of Russia from 11 .07 .2005 г .When crossing the border of the Russian Federation by children under the age of 18 (regardless of whether they are entered into the passport of the parents or not) accompanied by both or one of the parents (guardians, adoptive parents, trustees), you should have a document certifying the relationship (birth certificate, certificate of birth guardianship, marriage certificate, divorce, paternity certificate and t .д .) . In your case, of course, it is recommended nevertheless to issue a notarized consent to leave the father.