Adam and Eve's sin was disobedience. Lacking knowledge of good and evil has nothing to do with it. In fact, they already had knowledge of good from walking with God and having all good things provided for them.
They also knew, again from walking with God, that they were not God - that there was a significant difference between their abilities and His. For example, God created; Adam got to name.
The temptation to be as God was an obvious falsehood they would have known to reject.
God knows the highest expression of Good - Himself - and the absolute pit of evil that exists where He is not, but God also has the ability to know all these things without being corrupted by the knowledge in any way. He has the omnipotence and omniscience to ensure His plan always works out in the way that brings the greatest good (His Glory) before mankind.
Adam and Eve were created as moral creatures - similar to God's moral nature - else they could not have known God as Good, but they did not have God's power to not be corrupted by this knowledge. For them, the fruit of the forbidden tree was a virus.
Squirrels get all the peaches off the trees at my lake house. If a squirrel had eaten the forbidden fruit in the Garden, God would not have cared. They have no thought of being God.