While the birth of Wanda and Vision's twins seems to be a path to devastation, there's a spotlight on the horizon! Like in the comics, Billy and Tommy come into the world thanks to magic, though WandaVision hasn't explained what magic as of yet. But in the comics, it's the very same magic that leads to the babies' untimely deaths: their souls are reabsorbed into the demon Mephisto. In a cruel, but a fair twist of fate, they destroy him and their souls are reincarnated as Billy Kaplan and Tommy Shepherd.
Our theory for WandaVision is that when the couple learns that their "reality" isn't real and their children are figments of Wanda's power. The true mastermind (most likely Mephisto) will reveal that they wanted that power, and much like the comics, they'll attempt to absorb the "babies" but be destroyed by Wanda. Billy and Tommy will return (because of magic and reality-warping) and ultimately become the superheroes Wiccan and Speed. This will lead to the eventual formation of the Young Avengers (comprised of mutants from different multiverses) with Stature, Hawkeye, Miss America, Hulkling, and Iron Lad, all of whom have been announced or alluded to in other projects.