Short answer: Loki had three children with the giantess Angrboda: the wolf Fenrir, the serpent Jormungandr, and Hel, who rules the dead. He also bore a fourth child himself, the eight-legged horse Sleipnir, and had two sons, Narfi and Vali, with his wife Sigyn.
Odin heard the prophecy before any of those children could walk, and he dealt with each of them in advance. Every single precaution he took is what made the prophecy come true.
Fenrir: the wolf the gods raised themselves
Rather than leave the cub among the giants, the gods brought him to Asgard and fed him there. He grew so fast that only Tyr still dared go near him. Twice they tried to bind him with iron, framing it as a game of strength, and twice Fenrir snapped the chain and enjoyed the applause. The third fetter, Gleipnir, was made by dwarves out of six impossible things: the sound of a cat's step, the beard of a woman, the roots of a mountain, the sinews of a bear, the breath of a fish, the spittle of a bird. It looked like a silk ribbon. Fenrir smelled the trick and agreed only if someone would put a hand in his mouth as a pledge. Tyr did. The ribbon held. Tyr lost the hand, and at Ragnarok Fenrir breaks loose and swallows Odin.
Jormungandr: the serpent that outgrew the sea
Odin threw the second child into the ocean that surrounds the world, presumably to be rid of him. The serpent simply kept growing until he encircled the earth and could bite his own tail. Thor met him twice: once while fishing, when he hooked him and was stopped from hauling him up, and once disguised as a cat Thor could not lift off the floor. At Ragnarok they kill each other. Thor crushes the skull, walks nine paces, and falls dead from the venom.
Hel: the daughter who was given the dead
Hel was sent down to Niflheim, and Odin handed her authority over everyone who dies of sickness or old age, which is to say almost everyone. Only the battle-slain go up to Odin. She is described as half living woman and half corpse. Making her a queen was meant to keep her out of the way; it made her one of the great powers of the cosmos. When Baldr dies it is Hel who sets the price of his return, and the price is never paid. She sits beside the other rulers of the dead in Hades vs Anubis vs Hel.
Sleipnir: the child Loki bore himself
A builder offered to wall Asgard in a single winter, helped only by his stallion Svadilfari. Loki, who had talked the gods into the deal, turned himself into a mare to lure the stallion away and stop the work. Months later he came back with a grey foal that had eight legs. Loki gave Sleipnir to Odin, and Sleipnir became the best horse in the nine worlds. He is the one child of Loki that Odin kept close instead of disposing of.
Narfi and Vali: the sons of Sigyn
When the gods finally punish Loki for Baldr's death, they take his two sons by Sigyn. One is turned into a wolf and tears the other apart. The dead son's entrails are hardened into iron and used to bind Loki to three rocks, with a serpent fixed above his face to drip venom. Sigyn stands there holding a bowl to catch it. Every time she turns away to empty the bowl the venom falls, Loki convulses, and the earth shakes. The sources disagree on which brother had which name, and Vali is also the name of a son of Odin. More Norse context in our Norse mythology summary.
Every child of Loki at a glance
| Child | Mother or origin | What they become | Their part in Ragnarok |
|---|---|---|---|
| Fenrir | Angrboda | Wolf bound with Gleipnir, at the cost of Tyr's hand | Breaks free and kills Odin |
| Jormungandr | Angrboda | Serpent that circles the world | Kills Thor and is killed by him |
| Hel | Angrboda | Queen of those who do not fall in battle | Sends her dead in the ship Naglfar |
| Sleipnir | Loki himself, as a mare | Odin's eight-legged horse | Carries Odin into his last battle |
| Narfi | Sigyn | Killed by his own brother | Dies before it; his entrails bind Loki |
| Vali | Sigyn | Turned into a wolf | Dies before it, as an instrument of the gods |
Quick questions
How many children did Loki have?
Six in the surviving sources: Fenrir, Jormungandr and Hel by Angrboda, Sleipnir whom he bore himself as a mare, and Narfi and Vali by Sigyn.
Who is the mother of Fenrir, Jormungandr and Hel?
The giantess Angrboda, whose name means something like "the one who brings grief". Loki's own mother was Laufey, which is a separate story.
Did Loki really give birth to a horse?
Yes. He changed into a mare, was covered by the stallion Svadilfari, and later gave birth to Sleipnir. The sources treat it plainly, as a thing that happened.
Fenrir's binding, Thor's fishing trip and the night the gods bound Loki, told as audio dramas in MythologyNow.
