Never assume anxiety is all pyschological. Rarely does anxiety or depression stand alone as they are often times *symptoms* of underlying condition. Of particular concern is age, when a young child exhibits anxiety, a medical cause should be the first sought out. The case of my 9 year old having anxiety was resolved when it was found out he had a thyroid issue as both hypo and hyper thyroidism can and do cause anxiety. My own issue was Graves disease undiagnosed as a child and teen and I wouldn't wish that suffering on anyone. Deep breathing and positive thoughts simply do not work when a medical condition is at the root. Low iron, vitamin B-12 and a host of other endocrine concerns and vitamin deficiency may be at play along with neurological concerns found in spectrum disorders, mild autism and ADD/ADHD. Sadly many Drs are not well versed on Endocrine issues ( often reading testing results incorrectly assuming that *in range* means fine) nor regularly test for vitamin deficiencies. The other issue is a lack of definitive proper ranges for children. Much research still needs to be done. If the issue be psychological in nature then no harm done in getting full medical testing, however, assuming emotional issues are simply personality disorders or pyschological in nature can be dangerous as physical issues will persist and worsen. If autoimmune disease is an issue in close relatives, be suspicious...very suspicious!
Take heart, anxiety can be controlled whether medical or psychological in nature. Its about doing your research, getting all medical results in hands, questioning and being persistent.
I wish you both the best!