Okay first I'm not trying to scare you. I have a child who's 3 and I would not intentionally scare a mother. It could be growing pains, these are real. But, one of the signs of leukemia is leg pain that is sharp enough to where a young child would complain. It is probably something little, but please go to the doctor to check.
Growinqq pain. My little brother had the same thinq. My mom asked his pediatrician on his visit to qett a shot, and they did tests and thenstold her it wasnt anythinq to worry about and was just qrowinq pains. Hope i helped :D