At the start talk to them about what they like dislike and what they want to improve on. Then focus on this.
/let the three girls on the ground give a lesson to each kid so they see what they are looking for.
We used to do jumpig games of top score and chase me charlie which was so much fun and suer competitive.
Practice first aid and hoof care. What to look for on daily checks,
How about a walk where they each have a camera to take pictures of dangerous plants and make a journal.
Watch a video such as thrills and spills is always good!
Maybe make horse treats?
Do anatomy classes and conformation