Please teach your son to pray just a few simple prayers (with attention, not like a poem or a tongue twister), especially "O Lord Jesus Christ, have mercy on me, a sinner". Explain your son what the prayers are all about. Don't force him, but show a good example. Pray together with him. (Try to receive communion together with your son too).
Tell your son that we pray so that God can help us to become more like Him in our actions:
• For renewal and the growth of our soul.
• To give thanks to God for all he provides for us.
• To seek forgiveness for our sinfulness as humility is a prerequisite for prayer.
St Isaac the Syrian says that we should:
• Pray with attention – so that we can have a true encounter with God
• Pray with humility – because this sort of prayer goes straight to God’s ear
• Pray with affection and tears – with joy and thanksgiving, but also with true repentance and purity.
• Pray with patience and ardor – ‘to deny oneself’ is courageously to persevere in prayer.
• Pray from the depths of the heart – even if we pray using ‘the words of another’ they should be uttered as if
they are our own. St. Isaac says this is especially true of the Psalms.
• Pray with faith and absolute trust in God – because He knows our life.
So pray together with your son, raising your heart and mind to God, i.e. from the depth of your heart, with attention, humility, reverence, and repentance. Pray for your son, for his friends, parents, and relatives, and everyone he wants to pray for.
You may also tell him that church is a special place of God's presence, where everything is arranged to make his prayer stronger. An Orthodox church (temple) is the best place for prayer. (Where else we can pray for two hours?) Let your son pray during the Liturgy. Pray together with him. Don't do it out loud, of course, but please do pray.
When I don't understand singing during the Liturgy, I always pray the Jesus prayer: "O Lord Jesus Christ, have mercy on me, a sinner" or "Lord, have mercy". And the 2-hour liturgy runs as fast as it if it were 1 hour or sometimes even 40 or 20 minutes. Prayer (with attention, humility, reverence, and repentance) is the key.