Holding a player's attention during practice and throughout a season is a coach's biggest challenge, regardless of their age. Structured practices and regular communications are important. Being flexible though is even more important. US Soccer's Grassroots framework outlines this balance as "Play, Practice, Play". This provides a sequence of playing as soon as players arrive (1v1 and expand as players arrive), focus on skill development, and apply it in scrimmages.
Beyond building the expectation of "having a plan" in each practice, have fun with the team. Your players will mimic your behavior, energy/dullness, and excitement. If you have to break your plan a bit to focus more on a a particular area or roll with something funny that comes up, do it. Focus on getting as much of your plan accomplished while ensuring everyone walks away a better, and happier player.
As their coach, I've always tried to make it fun and let them grow into a "self coaching" environment. The coach is responsible for the team while the players can shape what they want out of the team more and more as they mature. As they are coaching themselves now, I see what we've learned together shining through. This is the leadership skill that I've hoped each player can develop. Show them they can make a transition from passive learning to active learning.
Build some structure while being loose with it. Have fun.