The are dozens of available drills and challenges that you can use to structure trainings at all Junior levels.
Junior Framework Manual gives and outline of the balance that a training session should achieve between General Movement (warmup), Coordination and Technique drills, and Small Sided Games with different challenges in them.
Junior Games & Activities is a big resource of drills to use.
Additional Junior Games & Activities are more, interesting drills.
For specific age grades:
And if you are looking for a specific challenge for a player or competition within the team to improve a specific aspect, try one of these: