Take this isolated island country, about the size of Ireland. The technology and society can be compared to 17th century Western Europe. The country is densely populated, and the people have lived on that island for as long as they can remember. No other landmasses are known.
A very small portion of these people is able to 'enchant' people. I'm still looking for a right verb, but the weak version of the power is that they can subtly compel people in general to do what they can to please them. By applying their power more forcefully, they can fully possess an individual; take over someone's body for up to a few hours at a time (which the possessed person has no recollection of afterwards).
Here's the thing: for the people who have this gift, power is inversely proportional to age. What that means is that in the population of a couple million, a few dozen to a hundred babies every year will be born with this power. Promptly they will, voluntarily or not, turn their entire environment (the range is a few hundred meters, regardless of walls) into their servants and grow up treated like royals.
This early period has a high mortality rate: some of these toddlers overdose on their magic and die of brain aneurysm, some get over-confident and are slain by someone they cannot enchant (a similar fraction of the populace is immune). A handful perishes simply of the excessive luxury, e.g. from obesity.
Those who survive into childhood tend to grow mature enough to control their power and apply it with more measurement, as it grows weaker. A magician in their teens is at their most 'effective', because although they must take weeks between total possessions and their subtle power only serves to make them generally considered likeable by people in their vicinity, they are now skilled enough that they can go a long way with a few enchantments here and there to clear any obstacles in their way. No magician in their twenties has any meaningful amount of power left.
So the magic teens are effectively the ruling class; they are organised and through selective magical manipulation of the real power holders in the country they keep their class living in luxury. Every now and then they make other kinds of interventions, like to prevent war or revolution. However, their influence is hidden; the populace would never tolerate being ruled by a society of magicians, especially magical children.
So they have two objectives: firstly, every new magic baby needs to be found as soon as possible; they need to be protected against themselves, and educated not to over-use their power so as not to ruin the masquerade. And the second objective is to provide a reason for this whole situation where extreme social mobility seems to exist for a handful of toddlers each year, who are born peasants but end up in high society by puberty.
Because this class of a couple thousand kids and teens has enough power at their disposal to manipulate key figures, a logical path is to focus on the priests. Establish a religious doctrine that explains them and presents their influence as a good thing. My first thought was a dogma that powerful spirits dwell in afterlife, and that every now and then they touch an Earth child and imbue them with their power. But an issue is that this draws attention to the child itself; it sets positive expectations on them (people will wonder how the child or the spirit could help them) as well as negative expectations (because power draws envy and use of this power tends to be for selfish reasons, people would grow to hate the spirits and the children with them).
Enchanting is a relatively nasty form of magic, in that it violates other people's agency. What's more, the general population is be growing more cynical each year; it is age of enlightenment, science is on the rise, and people are getting tired of dogma.
What could the magical teen caste do to help preserve their powerbase, and explain the magic babies that enter their ranks every year, in a manner that does not reveal the true power of the caste nor does it draw unwelcome attention to themselves or their 'fresh recruits'?