You should gather all team members for an internal evaluation. Before this meeting it is highly useful if a team member has already gone through the participants’ feedback, so these valuable comments can be included in the discussions. If you are doing multiple face-to-face events you should learn from their feedback and adjust your activities accordingly.
Regardless if the activity is face-to-face or online, the key word in this phase is: Follow-up! You should keep the young participants updated on the progress of your project. You should communicate the results of the event and explain how they have already been and will be used. You should do this to demonstrate that their contributions matter and keep them engaged in the project.