My 5 year old nephew's blood report says hemoglobin-7, tacked cell volume-23%, WBC count- 11500, platelet count-179000, esr-07.Is it a thalassemia?

Insufficient info. With a hemoglobin of 7 he is not likely to have major thalassemia. There are many causes of anemia and treatment would depend on the cause. The doctor who ordered the tests should be able to advise. You may visit this site for more info on this topic. http://www.chw.org/display/ppf/docid/21855/router.asp.
No way to tell. There are a lot of thalassemia variants. The hemoglobin is low for beta thal minor, high for beta thal major. What matters is that your nephew is seriously anemic and as a responsible adult you need to see that he gets diagnosed and treated.
Anemia. These blood counts show an anemia (decreased red blood cells) but the tests needed to determine if this is from a thalassemia or another cause are not listed. It is important to determine why there is such a severe anemia and would recommend seeing a hematologist.