Isaiah came to me one day, a little bit anxiously, and asked me, "Mom, what if God talks to me, and I don't hear Him?"
"Isaiah, usually when God talks to someone, and that person doesn't hear Him, God speaks again until he does hear Him." Then I told him the story of Samuel. He seemed relieved.
Later, I was snuggling him as I put him down for a nap, and I asked him if he wanted to pray for the Holy Spirit to make him strong to do what God wants him to do.
He said, "But what if God wants me to go in a war to fight the bad guys? I'm just little, and I can't shoot those bad guys."
"Isaiah," I said, "God is not going to ask you to go fight in that kind of a war when you are just a little boy. You don't have to shoot bad guys. But you can be a mighty warrior for God in a different way. By praying and learning God's Word, you can fight spiritual battles, even when you're very little. God can make you very strong to do it."
He smiled hugely, and said he did want to pray. "Jesus? Will you give me help from your Holy Spirit to do what God wants me to do? In Jesus' name, amen."