Hi yam655! Welcome to Discourse.
I started teaching my daughter coding when she was in the first grade. The only prerequisite is the ability to read. Getting the most out of Code Combat just involves doing it. Learn the concepts each level is designed to teach and try not to take short cuts just to finish a level. Each child will need their own account. The best deal is the lifetime access, which has all the subscriber levels. You can always use the free version, but it doesn’t have as many levels to help drive the concepts home. Also, subscribers have access to contact the Code Combat staff for assistance.
I believe that there is a way to sign up as a teacher and then have your children as students where you can monitor their progress from a central point. I’ve never used this so I can’t be much help with how this works. @stephanie is the Customer Support Representative and liaison here. She can be of more assistance with the use of the teacher/student setup.
BTW, I am a volunteer moderator on this board and a user of Code Combat. This is the place to ask for assistance if you get stuck on a level.
Good luck and have fun!