Apart from the Biblical Proscriptions listed below, there is a danger in opening your household to other spirits. Nobody thinks evil will come to their house until it does. Once in it often goes after those least able to defend themselves (…the little one’s). You are asking because your gut is telling you something is not ok. Even if he plays at a friends house, spirits can come home with him.
You will know the level of infiltration by the level of resistance you receive if you suggest he stop.
“When you come into the land that the Lord your God is giving you, you shall not learn to follow the abominable practices of those nations. There shall not be found among you anyone who burns his son or his daughter as an offering, anyone who practices divination or tells fortunes or interprets omens, or a sorcerer or a charmer or a medium or a necromancer or one who inquires of the dead, for whoever does these things is an abomination to the Lord. And because of these abominations the Lord your God is driving them out before you." ESV
CCC 2117 All practices of magic or sorcery, by which one attempts to tame occult powers, so as to place them at one’s service and have a supernatural power over others - even if this were for the sake of restoring their health - are gravely contrary to the virtue of religion. These practices are even more to be condemned when accompanied by the intention of harming someone, or when they have recourse to the intervention of demons. Wearing charms is also reprehensible. Spiritism often implies divination or magical practices; the Church for her part warns the faithful against it. Recourse to so-called traditional cures does not justify either the invocation of evil powers or the exploitation of another’s credulity.