Supernatural Faith in Jesus Christ is required. Jews, Muslims, Buddhists, pagans, etc. do not have this, and they cannot be saved without it. Is not it written,
"Everyone who believes in the Son will not be judged. But everyone who does not believe in him is judged already, because he does not believe in the name of God's only Son." (John 3:18)
So that means if a mute or infant is baptised...and he can't say with his mouth..."'Jesus is Lord"...then he's damned, right?
Is that what you're saying?
An infant can only be saved from Baptism; a mute may not be to say with his mouth, be he/she could still write, sign, or at least, nod, so yes, mutes can be saved, if they believe.