I've had headaches all my life, including when I was a child. Vision is an issue when the eye muscles get weak (they call it poor convergence), apart from that i suffered physical stress headaches/migraines almost daily. Even bright lights, loud noises etc makes it worse. It was not so severe as a child but it got worse later.
When a child or underweight person is tired, the body can tense up, if the neck/back muscles spasm or get stiff, it can trigger daily headches for no other reason. I noticed that when i take complete rest for few days, I dont get headaches at all.
Anemia also causes me headaches if its very low. I cant get a clear understanding of reports, But with iron supplements my hgb maintains at 9 to 10, and without iron, i have even gone as low as 8.3.
Sometimes even daily headaches can become a 'habit' for the body. What that means is that the body gets used to tensing up - in that case, relaxation, exercise, stretching, eye exercises, etc can all help.