Recently my 3 year old has been sensitive to films with 'bad guys' which I believe refers more to scariness than to antagonistic roles, but hasn't wanted to watch the OT for a while.

So we've taken to watching the LEGO: Star Wars films, "Padawan Menace" and "Empire Strikes Out." He's really into them, and a 3 year olds perspective on what's funny is great.

"Darth Vader doesn't like being silly?"
"Princess Leia says Go!" (his favorite part)
"Does C3PO like having a bat?"
"Why does Darth Vader's friend shock him?" (Palpatine)