Vasilii is the only known immortal child in the series, at least the only known by name. He was created by Sasha, who also the founder of what would become the Denali Coven. Sasha and Vasilii were killed by the Volturi, because Meyer needed a reason to create the last book, and not bore her readers to death by not pretending to have a plot. Needless to say, she never delivered said plot anyway.
But the kid is kind of cute right? RIGHT?! (He's still a Meyerpire, after all, and therefore he is super beautiful and cute.)