It is generally believed that if a pregnant woman goes outside during a total eclipse, and with no clouds to protect her from the 'black rays' of the sun, she runs the risk of her baby being born very frail and sickly, half-witted, mad, or more than one of these, and with an inborn magical talent.
Such children will excel in areas of magic which match their spirit. One who rains fire and death on their enemies will be quick to anger and blame. One who excels in illusions will be a font of false oaths and promises, and a leader-astray of the innocent. One who begets madness will themselves be mad. It may be that this could work the other way, with virtuous spells matching virtuous magicians: but such would be a rarity of rarities.
They are also said to excel in the learning of languages. They are sometimes said to be able to learn languages without even hearing or reading them. Though, alas, they have little of sense to say in any tongue.