The Talmud and Zohar talk about demons. Ultra-Orthodox Jews certainly believe in the existence of demons, and, to the best of my knowledge, so do most Orthodox Jews. Rambam/Maimonides in “Guide for the Perplexed” claims they do not exist, but the Vilna Gaon, among others, take Rambam to task for this view.
As for Lilith, she is considered the queen of the demons, sort of an anti-Shekhinah. I don’t know if harming children is one of her duties or pastimes, but she is not the only demon who does this.
As for things on the Internet sounding like mythology, well, probably because we have as much first-hand experience with Lilith & Co. as we do with Zeus and his friends! 🙂
kol tuv (=all the best)