3 year old son with history of poor weight growth. Labs show burr cells1+, high ast, low bilirubin, low hemoglobin and hemocrit. Ideas?

Depends. The labs might reflect the cause of poor weight gain or reflect that the child is not optimally nourished. Best bet is to follow up labs with the doc who ordered them.
Talk to doctor! This type of situation needs a thorough discussion with the child's doctor. Blood test results should be interpreted with knowledge of the child's history, family history, and physical exam findings as well as the specific findings and rationale for the tests themselves. Good luck!