Jesus tells us that the greatest in the Kingdom of Heaven is the person who will humble themselves like a little child in regard to their faith. Not child-ish, but child-like faith is required for us to have the best possible relationship with God. This means coming to God with our needs, and allowing him to fulfill them in His way and His time. This means being humble enough to say "I can't do this on my own." It means having a tender heart towards God and receiving his teaching, correction, and discipline.
Jesus also says whoever welcomes a little child in His name, welcomes Him. We need to welcome little children into our lives. We need to recognize their value and help to meet their needs, both spiritual and physical.
Jesus tells us to let the children come to Him and not hinder them. Not all of us are called to children's ministry, but all of us are called to minister God's love and grace to the children in our lives. We are to live the abundant life in front of them so that when the time is right, God can draw them to himself and give them that same life in Christ.