On a playground, a sandbox is a place where the dirt is cleaner than the dirt that is found naturally around it. No roots, no weeds, less dangers. It is a created space, where the environment is different.
One method of creating leadership is to create space in front of a younger generation in which they can sandbox, to learn and create and fail and learn. Trusting them with things that would be beyond their reach without the help of the Holy Spirit can teach them to listen to Him. Trusting them in a space where the current leaders are present for advice and repair is a safe place for them to learn to make decisions and to follow through with them to discover the outcomes they produce.
Frequently the narratives about the ministries of Jesus imply that He sent disciples out to fulfill assignments and taught them how to do it when they returned with questions their experiences had prompted them to ask. Our methods are usually to give classroom instructions, written exams, and then exercises in labs before we trust anyone with real work. They have to prove something before we trust them with responsibility.
His plan seems to be to teach them to listen to Him.