I believe children are so great to Jesus, and He was saying that all people should be as innocent as little children and make a change in their lives to be like them, or they will never enter the kingdom of heaven; Matt 18:3. He goes on to say, "the greatest person in the kingdom of heaven is the one who makes himself humble like a child" (verse 4).
I think that God can and will use kids who make themselves available to Him. That reminds me of a letter that Paul wrote to Timothy telling him in 1 Timothy 4:12; "Do not let anyone treat you as if you are unimportant because you are young", and he goes on to say, "Instead, be an example to the believers with your words, your actions, you love, your faith, and your pure life". I believe that is what God wants all young people to understand and do.
We can read in this story that Timothy was taugth from the Bible as a child by his Godly mother and grandmother. He grew to become really attracted to Paul, because Paul lived a life that was probably closer to the way Timothy was taught than anyone he had ever known. It may have been that he didn't have a dad to teach him the proper ways to live. He became very close to Paul, and Paul became close to Timothy. Timothy grew and became a spiritual leader to the church at Ephesus. He became a perfect witness to all the people by doing exactly what Paul asked him to do. In that way, God used Timothy, and he can use you too. God is no respector of persons and your age doesn't matter to Him. He uses all who make themselves available for Him to use. Above Scripture comes from The New Century Version.
Following Scripture is NIV
Jesus Christ wants children to come unto Him. Mark 10:14-15
God loves children and sent Jesus to earth for them. John 3:16