Pediatric neurology question? Can kids have nosebleeds from stress? Happened a few times in child under 6

Anything's possible. But it's far more likely, and common, for kids to have nosebleeds from nose picking.
Not common. Stress is an uncommon cause of children's nose bleeds. They are usually caused by mild trauma to the lining of the nose. Stress might cause a child to rub at their nose or pick at it to cause the bleeding.
Nosebleeds . Kids pick noses and the capillaries in nose are very delicate. If they sneeze the nose can rebleed. If they have increased stress their blood pressure can increase as well and then delicate vessels can re bleed. Allergies can worsen this as well. If you think he is stressed then help them manage their coping mechanisms. Their pediatrician should have good contacts for this. Hope this helps.