I think my friend's 5 yr old may have lukemia, what are the early signs?

Well, the symptoms of leukemia are broad, but there are specific symptoms of leukemia to keep an eye out for:
1) fever
2) infection
3) excessive bruising
4) fatigue
5) physical exercise intolerance
6) abdominal pain, or generally feeling fullness
7) weight loss
abnormal bleeding
9) enlargement of the lymph nodes, spleen, and/or liver
10) weakness

Leukemia usually occurs on people over 25 yrs old..but you know, when it occurs on children, it usually happens before the child is 4. So don't worry too much:)

Bone cancer? or blood cancer, that is leukemia. I hope that your friend has taken the child to the doctor. If caught early, childhood leukemia has a very good cure rate.