Teaching him in Religious Ed?
Is he enrolled already in the church Sunday school classes?
If not, he should know the Sign of the Cross, how to bless himself with Holy Water, the Guardian Angel Prayer, how to sit in church during Mass without having a meltdown, the Hail Mary, the Glory Be, and beginning the Our Father.
He should have a basic knowledge of Jesus’ love for us, and his resurrection.
The Nativity story, heaven as our goal, that Sacraments give us grace, and are the tools for holiness. He should be told about his Baptism, and how he’s a special child of God.
What series does you parish use for Religious Ed? Maybe the DRE can give you some materials if he’s not already been going regularly.
Have fun!