"Anxiety also presents in different forms. Common ways that anxiety manifests is avoidance behaviour, worries, self-doubt, excessive fears, and social anxiety," said Sharma.
Take a look at the sorts of things they're worrying about, and the severity of those worries. Is it hindering them from other aspects of life? Are they avoiding certain school activities because they're worried about something bad happening? Or worried about what the other kids might think?
Keep in mind that it's healthy to worry about certain things, so you'll have to use good judgment. "In many cases, feeling anxious or nervous is normal."