the most prominent case is daenerys’s son rhaego, who we know was born during a blood magic ritual. mirri maz duur describes rhaego as draconic (“He was scaled like a lizard, blind, with the stub of a tail and small leather wings like the wings of a bat. When I touched him, the flesh sloughed off the bone, and inside he was full of graveworms and the stink of corruption.” AGOT Daenerys IX) which comes after mirri maz duur as performed blood magic to save khal drogo’s life. the premise is simple: only death could pay for a life. it’s easy to assume that the horse would have been enough for mirri maz duur to heal khal drogo as was originally implied, but it’s heavily implied that rhaego’s death is a result of her as well since she handles daenerys’s birth. in the book, it’s left a little more for interpretation but in the television series, mirri maz duur outright admits to killing rhaego.

it’s worth noting the other cases have viable proof of blood magic interference as well. maegor i targaryen notably struggled to produce heirs and one of his wives, tyanna of the tower, confessed to poisoning alys harroways who had birthed a child (Maegor came to see the stillbirth, he was horrified to find the boy a monster, with twisted limbs, a huge head, and no eyes. Fire and Blood: The Sons of the Dragon.) the same would go for maegor’s bride jeyne westerling (Three moons before she was due, Queen Jeyne was brought to bed by a sudden onset of labor pains, and was delivered of a stillborn child as monstrous as the one Alys Harroway had birthed.  Fire and Blood: The Sons of the Dragon.) and elinor costayne (Queen Elinor too was delivered of a malformed and stillborn child, an eyeless boy born with rudimentary wings.  Fire and Blood: The Sons of the Dragon)

the only two instances where it could be debatable whether or not blood magic was used against a child are laena velaryon who died after complications while giving birth to a twisted and malformed son and rhaenyra targaryen who lost her daughter visenya after going into premature labor. rhaenyra seems to place the blame on the greens (“She was my only daughter, and they killed her. They stole my crown and murdered my daughter, and they shall answer for it.”  Fire and Blood: The Dying of the Dragons) which is likely due to the announcement of king viserys’s death and the crowning of aegon the usurper, and part of her grief. i’ve seen some people say that rhaenyra cast black magic herself during this because she “cursed” her half-siblings but this seems a bit like victim blaming and like its just on redd//it.