With my boys, now ages 15 and 17, they were taught from Day 1 all of the Eddie Eagle safety rules and these applied to all guns, real or toys (the toys that look like "real" guns- not Super Soakers and that sort of thing). My boys do not treat toy guns any differently than they treat a real one to this day.
When they were about 7 or so years old I gave them each a copy of the NRA Firearms Safety Rules and told them when they had them memorized then we would start working with handling real guns. These days they are absolutely some of the safest people you will ever see on the range.
Eyes and ears must always be worn when shooting. They carry ear plugs with them everywhere they go, and frequently eye protection as well.
Bad habits are very difficult to break, so if you see anything that will develop into a bad habit put a stop to it now. don't put it off until next time.