Sickle

Anyone who is "a Wizard" (the general term by the populace) is feared by everyone else. Nobles have a well placed respect for Wizards and many Wizards have aspirations of power. The only reason the whole world is not taken over by these often quite corrupt individuals is that they are so few and far between that they can't muster that force, and when their spells run out, they are often weak bookworms with no combat ability whatsoever.

Instead, a lot of the influence they have comes from intrigue and manipulation. Magic items are exceedingly rare and costs thousands of gold pieces. Nobody except nobles would spend the same amount of money on a sword as is the price for a decent apartment in Capitoleum.

The Sickle, which is the mage guild of all the Realms (specifically that means the Northrealms, Midrealms and Southrealms) has its seat in the Capitoleum in the Spire (what's with Wizards and their love for towers, ey?). It's maintained by Wizards, where the highest circle are called "The Administrators", which has been a problem with the rest of the city's administrations as they do not want to be confused with wizards.

There is a rumoured "black faction" within the Sickle called the Scythe. No evidence has been provided for this faction and the truth is that the corruption of individual Wizards is often so great anyway, so there seems to be no need for it, but people do like to gossip, especially about Wizards.

The rumour has it that some of them are unhappy with even being with humans so they summon demons and do dirty acts with, or sends up animals to their rooms and have their ways with them. They start this as Apprentices and that's why they never have children.

Regardless of what you believe, The Sickle has a tight rein of magic users in the Realms, and have people in most cities looking out for magic users. They even have a powerful spell that registers ALL use of magic in the biggest cities. Just as well because often parents are so afraid of their child if they develop magic potential they will turn their kids in themselves. When a Wizard returns to his home town, he's often change massively, which is thought to be because The Sickle brainwashes young children with demonic magic to make them more like them.

That's better than hiding the child though, because there are lots of stories where that happened and the child charged up magic so much until he literally exploded and killed not only himself but his family and sometimes the neighbours as well.

Magic items are ironically highly sought after and a massive status symbol, but the people feel they have many reasons to report magic behaviour if they notice it.