Little children are very trusting, dependent, innocent, and loving. In Heaven God's children will be trusting of His provision and care for all eternity. They will also be totally dependent upon Him, realizing that they have no power to provide any of their needs. It gives order to life and prevents gross immorality by each man having his own wife, and each woman her own husband. Marriage serves a number of purposes on Earth, such as, a picture of the relationship of Christ and the Church.
Marriage also provides a means of orderly procreation.
Also the ordained union of man and woman in marriage provides the means of physical pleasure on Earth, a true gift of the Lord. But in Heaven, immorality will not be a problem because there will be no evil, lusting hearts there. Often Heaven is presented as a place where there is nothing to do. In Heaven we will rest from all the struggles and problems of this life on Earth, but one will not vegetate. For evidence of this, one only needs to look at the Scriptures.