How can I prevent my kings from changing their succession law within the empire?

I play as a High King of the North Sea, and I like to give titles to my children pre-emptively so that they learn to rule.

My problem is that my children have a preference to almost immediately enact Scandinavian Elective law with their king title and thereby are completely removing the direct family from the succession. (At least the title often goes to someone in my dynasty.)

I, as a player, don’t add any laws to my titles. And I don’t want my heirs to enact those laws.

I once revoked a title from a rebellious king of England, and that way I had to spend prestige in order to destroy the law.

From a roleplaying perspective, the entire empire should be family business and that’s why I don’t want my kings to change the law without my consent.

Is there anything I can do or are king-ranked characters always able and willing to change the law?