Do you ask your kids to read a "real" book for 10 to 20 mins every school day? Our school "requires" parents to do so and it does seems to help with my kids time on task and focus. Note: "real" in the sense of not screen based. Anything with a screen is going to come with built in opportunities for distraction.
As a family, we also play games like "Exploding Kittens" and "Hearts". My youngest has asked about what it was like to play "D&D" and I think that they will be ready for something like The Princess Bride RPG. https://www.kickstarter.com/projects/toyvaultinc/the-princes...
Really, any thing that encourages engaged thoughtful imagination rather than passive entertainment is probably going to help.