Correct Sonny. Vito so much as admits it at the Solozzo meeting when it becomes clear that he can't even control his own son and heir apparent who is trying to negotiate the drug deal with Sol AFTER Vito has said "No." Vito says something like, as you can see I have a sentimental weakness for my children." He is admitting to Sol and everyone else that he is lettting sentiment and weakness get in the way of sound business judgment. If he knew Sonny would react that way he should have warned him in advance or kept him out of the meeting. Even Fredo, who was at that meeting, had the good sense to keep his mouth shut.