My 6 yr old has had pain in her legs, feet and ankles for the past few months she has a positive ana and a high esr what can cause this?

Autoimmune disease: You need to see a rheumatologist asap. This could be the earliest signs of juvenile rheumatoid arthritis or any of a number of serious autoimmune disease entities.

Autoimmune disease: A number of autoimmune disease can have those abnormal lab results. Your best bet is to see a rheumatologist, preferably one who specializes in kids. It is likely your daughter will need medication.