Unfortunately, in young, prepubertal kids, we're seeing eating disorders. The cause of it is unknown. There is conjecture again, in part. Speaking with some adolescent medicine colleagues and asking them the very same question, one of the theories is that during a period of time in this pandemic, with no sense of control, it was the one thing that they could control.
Other theories include online learning, dissatisfaction with their image and social media.
There are a number of theories, but we don't know 100% for sure.