If there isn't a bad or low mood, there is no depression. The depressed person feels sad even in pleasant circumstances, is often tearful for no particular reason, does not enjoy normally pleasurable activities. Anxiety is the medical word for unreasonable fear. If a child is afraid of a large, aggressive, and unfriendly dog, that's not anxiety. If he is afraid of all dogs, not matter how small and friendly, that is anxiety.
Some children suffer from what used to be called overanxious disorder.
This is now part of Generalized Anxiety Disorder, but the overanxious name is still a very apt description of the child who worries excessively about everything. Overanxious children often have bodily symptoms, particularly stomach aches and headaches. They may experience diarrhea or constipation, sleep poorly, have appetite problems, even worry themselves into low grade fevers. If a child has a lot of physical complaints but is not fearful, and does not worry unrealistically, she does NOT have an anxiety problem. Malingering means deliberating avoiding work or school.