A bump on head is harmless in adults. In children, especially toddlers who try to walk and run, may fall and bump their head. It is not a matter of concern unless they don't stop crying, become restless, complain of headache or ache in neck, vomit or don't function the way they did before falling e.g. staggering or uneven gait, inability to speak properly etc then it is necessray to consult a doctor. Commonly, a bump on head does not cause serious problems.