Serving the Lord means doing all as unto Him.
It does not mean having to be in a recognizable Christian position. I have known missionaries and pastors who were tremendous saints. I have also known some choice servants who served the Lord without recognition and in the most pedestrian of circumstances.
Children must be taught to serve the Lord. They should learn to sing when they are afraid, to give of their money, and to encourage others. Children who have given their hearts to the Lord should be taught to pray privately and to do so aloud. They should understand the purpose of life is about the Lord and that it is not about having a good life.
Children should be taught to visit sick friends and encourage Christian friends. Regularly. It should be the normal thing to do.
A good children's church is fine. That is, if the purpose is to train Soldiers of The Cross. Children must understand the most basic tenants of the faith and not be separated out, only to have a better time. They must learn that when they are saved, they are members of the Body of Christ. They need to see mature Brothers and Sisters in prayer, in song and in service. They also need to hear anointed preaching.
Children need to hear and memorize the real Word of God and not watered down versions. The intellect is not the interpreter of the scriptures, but rather the Holy Spirit.
They are not our children.
They are His.