The first requirement is "to turn." The NIV translates it "change." It is translated many times to refer to the act of changing one's ways to turn back to God implying repentance, confession, and asking of forgiveness. My worst offense to God is the sin of self-sufficiency. God created me to depend on him and when I set out to live a life independent from him, I spit in his face. Children are totally dependent on their parents. If I want to be great in the kingdom of God, I must turn from my self-sufficiency into dependence on God.
A second characteristic of children is that they are innocent. Innocence as to be pure from evil. Jesus (Mat.10:16) and Paul (Rom.16:19) used childlike innocence when it comes to my relationship with evil. I am to be wise as to what is good, but simple as to what is evil. It does not mean that I am to be naive about evil, but that I don't practice it. Unfortunately, I am tainted by evil and I need God to transform me day by day to become less dominated by evil and more dominated by good.
Since I am not a child, but an adult, it requires great humility to be dependent and innocent. Therein lies greatness in the kingdom: in my willingness to humble myself before my King as to be dependent on him for everything in my life and to be innocent of all evil in this world. Unless I am willing to be like a child in this regard, I have no entrance in the kingdom of God.
Father, I am your child and I want to act like one as to dependence and innocence. Help me to overcome my self-sufficiency and my knowledge (practice) of evil. Fill me with your Spirit this day to walk with you held by your hand.