A kid that hasn't mature (baligh) or of age yet didn't need to worry on most Islamic obligation rules. They do had that good, even the sin of their wrongdoings goes straight to their parents. But, When they had their first 'wet dream' no more of that free ticket.
Do remember that this is still fiction and that at many points the things it has described has been off from what the actual traditions were (often it's clearly an oversight, and sometimes it seems, if not intentionally incorrect, then at least intentionally done for literary reasons without bothering to fact check for accuracy).
Though even having said that, it is very possible that it's as simple as him being royalty resulting in different expectations in how strictly he must adhere to his religion.
I thought the kid had congenital heart defect. Turned out it was anxiety disorder.
I was thinking asthma at first, until she said it was anxiety (I think this is the kind of manga where mc will likely always be right in their assumptions).
It's actually pretty tame tho. If it was more hardcore peace wouldn't be an option.
Sounded like they had to choose between peace or subjugation, so it would still be peace in the end.