My 4 yr old son has a small white bump hollow & slightly black in the middle on big toe. he says it hurts but doesn't complain constantly; 10 days now?

Bump: Four-year-old children should not have painful toe or toes. This sounds like a dermatologic condition and could be serious. You should have your child seen by a dermatologist or a podiatrist for an accurate history physical and diagnosis of this problem.

Sounds like : A wart but without seeing it i would recommend you visit a podiatrist or dermatologist.