I will show you the system that I have set up. I prefer to plan by the week, so I have 36 weeks to plan. If this works for you, great. If not, hopefully it will inspire you to create your own organizing system.
Hanging files (green)
File folders (red)
Sheets of labels
So in the Week 1 hanging file, there is a file that says "Child's Name 1". As I plan, I will place the lesson or activity in the correct child's folder for the correct week. You could choose different colors for each child. I chose to stick with just red and green for 2 reasons: 1-our homeschool room is all red and green and 2- I didn't want to spend the money on 3 different colors.