I don’t see you mentioning sports. Are your boys in any kind of organized sports? My son was in Little League baseball when he was 5 or 6 till HS graduation. He would admit that had a huge impact in his life. Being in organized sports is excellent in learning discipline, team play, cooperation, time management, coping with disappointments etc.
I also think it is too early to think about academics at this point, continue what you have been doing…you are doing a great job.