Your prayer for your son reflects the deep love of a parent's heart, and God understands that love completely. Scripture shows us that the love of a father for his son is one of the strongest pictures of God's own love. When God asked Abraham to offer Isaac, his only son whom he loved, it was a foreshadowing of what the Father Himself would do in giving His only begotten Son for us. God so loved the world that He gave His only Son, and because of that gift we can now be brought into His family. Through Jesus, born of a woman under the law to redeem those under the law, we receive adoption as sons and can cry Abba, Father. Your son is held in that same Father's care, and your intercession for him is precious to God.
You are right to pray for protection of his heart, mind and body, because our real struggle is not against flesh and blood but against spiritual forces. The enemy does seek to steal and kill and destroy, and much of that battle is for the mind. We may walk in the flesh, but the warfare is spiritual, and so the weapons must be spiritual as well. God has provided those weapons for us, and they are not carnal. They are the Word of God, faith, and prayer. By those we stand against the schemes of the enemy and see him defeated.
It is fitting to ask God to cover your son with the blood of Jesus, to station His angels around him and to make His presence a shield. Scripture promises that God gives His angels charge over His children to keep them in all their ways, and that no weapon formed against those who are His will finally prosper. That does not mean we will never face difficulty, but it means we walk in the safety of His presence and under His watchful correction and care. As a father corrects the son he delights in, so the Lord shepherds and keeps His own, and His discipline itself is a sign that we belong to Him.
Continue to speak the Word over your son, to pray with faith, and to give him the instruction of a godly parent. The wisdom given to a son to receive words, to incline the ear to wisdom and apply the heart to understanding, remains a path of protection. Even when a son wanders, as David's heart still went out for his son Absalom in rebellion, saying deal gently with the young man, how much more does our Heavenly Father's love pursue and guard. He hears a parent's cry.
I join you in prayer. Father, in the name of Jesus, I lift this son to You. Surround him as a shield, guard his heart and mind and body, keep him from the enemy's schemes and from harm and danger, let Your angels encamp around him, and let him walk daily in the safety of Your presence. Cover him with the blood of Jesus, strengthen his faith, draw him close to You, and let him know he is Yours. Amen.