The Child Hunts (子供狩り) are a practice of the Loptyrian Cult and, much earlier, the Loptyrian Empire in Fire Emblem: Genealogy of the Holy War in which all children between the ages of 7 and 13 are rounded up and are either sacrificed to the Dark God Loptyr, or forced to fight amongst themselves in arenas, with the surviving children crafted into nobles in what Julius and Manfroy hopes will be the new Loptyrian Empire. It is extremely prevalent in the second generation of Fire Emblem: Genealogy of the Holy War and in Fire Emblem: Thracia 776.
In Genealogy of the Holy War, the child hunts are discussed first, and from Chapter 10 onward, Seliph's army rushes to overthrow the Grannvale Empire in order to save the children recently collected which are about to all be killed in a mass sacrifice to the Dark God Loptyr by Julius himself. However, before he dies, Emperor Arvis secretly devises a plan to hide the children from Julius, and with the help of his attendant Felipe and Ishtar, the children were successfully hidden at a church in Freege Castle till Seliph's army arrives, and no one would try to seize the children before this due to retribution from Ishtar.
In Thracia 776, the child hunts are revealed to be extremely prevalent in the Manster District, and when Olwen is faced with the child hunts in Chapter 11x, she's so disturbed that she can no longer remain on the side of the Grannvale Empire and the Freege's. They are also explained more in depth during the beginning of Chapter 6. Two of Leif's teammates, Dalsin and Hicks, will join his group if they save Dalsin's little brother Yubel and Hick's son Maphy from the child hunts; additionally, the objective of Chapter 3 is rescuing four children trying to escape from them, one being Coirpre (a Holy War playable character).