Talk about starting them young!
My 3 1/2 year old son is CONSTANTLY coming up to me and saying, "I wanna help you work, I wanna help you sew!"
So he sits on my lap and holds his left hand flat on the material to the left of the presser foot, with his thumb tucked under his fingers, to avoid the "dangerous" needle.
Can't wait until he's big enough to do it on his own!