At that age, we would run variations of this drill. I would use either a speed hurdle, or small soccer done also as a point of reference for their backside. Set the object down on towards back leg. on command, they would slowly step back over the object, engage hip, get into a launch position and swing away. I'd usually have my son hold his swing at extension but they can also do it as a full swing. I like to ask the boys if they can feel the tension on their back hip once they do it correctly vs when they don't. You can do it off a tee, soft toss, angled toss, or front toss and run. A skater drill would also be similar in where they would basically hop from back to side to front side back to back side and then swing away.
I'd also used to get a piece of foam from one of our PT clinics and put on back side and tell the boys to push down into the ground as hard as possible to engage their hip. Lots of times they they don't know what to feel for, I ask the boys if they know what a corkscrew is and explain what that does, our back side/core should look close to that motion.
I liked doing this drill too, to help the boys know what the load portion felt like, basically isolating the steps of a swing. Hard to start doing more advanced drills if we don't have the basics. Pretty simple but I felt it was a great one, especially at early age.
Theres a bunch more you can find, Josh Cathcart has some great ones on YouTube also, hope this gives you a start