Depends. Kids get headaches (ha) from illness, trauma, stress, migraines, and more. Identifying a cause is sometimes easy (such as with illness- which might be treatable, like strep) but often a ha diary of any possible triggers is helpful. Include amount of sleep, foods/drinks, sunlight, noise, smells, and anything else you can think of. Diary days even with no ha to compare. Doc can then help sort out.
Maybe... Depends upon the nature of the complaint; and any other factors(trauma, illness, stress, etc.) so please monitor your child's symptoms and take him/her to the pediatrician for an evaluation! if the symptoms persist.
6 y/o is a concern. A 6year old complaining of headaches is a concern. Start with your pediatrician, who may refer you to a pediatric neurologist.