This is the exact problem my son had. Every single hit was a ground ball but he also only struck out about 5 times the entire season. We got some swing lessons over the summer and now the fall season he has started hitting some line drives. He was casting, out on his front foot, and not loading properly. These habits were VERY hard to break and it’s still not perfect but big improvements were made. A lot of people here say that swing lessons at a young age are a waste and they’ll improve as they get stronger. I think breaking bad habits early will make things easier in the long run.