fantasy. there are some claims of satanic cults sacrificing babies and doing rituals with them, these are false claims to scare people away from all pagan paths.
if you're looking for a more realistic basic, you could argue some Wiccan/Pagan mothers whisper a name in their kids ear after birth, or there's a Wiccaning where the child is presented to the God, Goddess, and community. this doesn't make them a Witch or anything, it's just a blessing. in theory i suppose someone who works with demons could present their child before the demon for protection or similar, but as a sacrifice no.