Can children under the age of reason commit venial sins? From my external observation, I think they can. I can think of several cases where my daughter and older son have known what was the right thing to do, and deliberately chosen not to do it. Also, when my wife and I discipline them, I don't get the idea that we're disciplining mere jumbles of instincts and passions, but that their intellects and wills are thrown into the mix.
So while I have no trouble believing that small children can't commit mortal sins because they are incapable of full, rational choice, I would think they could commit venial sins. Anybody have an answer for me?
Well, were I to hazard an opinion, I would agree with you, but not for the reason that you give. If a child is not capable of full rational choice, then he isn't capable of sin at all, even venial. Such things would be objectively sinful, but not subjectively.
So *IF* you have a child that is able to make willed, rational choices about right and wrong at an early age (and rational is the key word here, not choice), then he could commit venial sin. But as for mortal sin, the conditions are more stringent, and it would be rare for a child that young to commit one even deliberately. He'd have to know it could be mortal, and that whole concept is probably beyond a child under six.