when they are going to do an activity X , said ( i will go) ( voy a.... comer,dormir, salir).
Does not matter, what matters is the subject, I, you, we, them.
example.
English yo - tú - Ud./él/ella - nosotros/as - ellos/ellas
Presente I go, am going voy - vas - va - vamos - van
Futuro I will go iré - irás - irá - iremos - irán