Eating much more or less than usual
Does your child's diet fluctuate drastically? If you find that they are eating significantly more or significantly less than usual, it may be a sign of a mental illness.
A study was conducted at Duke Medicine on how certain eating habits can actually be a sign of mental illnesses below the surface. The lead author noted, "Parents are very good at identifying picky eating in their kids, but it's much harder for all of us to identify things like depression and anxiety because the internal workings of our children are hard to know. So picky eating could be a marker, especially in severe cases, for children who would benefit from an intervention that would not only help them with food but help them manage emotions more generally."
So, these changes you are noticing in your child's eating habits could offer insight into what's going on with them more than you know.