Tests on the 10 most widely used football helmets showed they did a good job of preventing skull fractures and bruising of the brain.
However, they only reduced the concussion risk by 20%, compared with not wearing a helmet.
And that included a helmet specifically sold as reducing concussions.
Experts say parents can help, because every helmet fits differently.
Dr. Rick Figler, an orthopedic surgeon with the Cleveland Clinic Sports Health Center, says, " Every helmet fits every kid a little bit differently. So, they need to make sure it fits good, that it is in good repair, that they wear it and that they use it properly, as well."
Doctors say coaches should also emphasize safer tackling techniques, and strengthening neck and shoulder muscles.
The helmets tested were:
* Adams a2000
* Rawlings Quantum
* Riddell 360
* Riddell Revolution
* Riddell Revolution Speed
* Riddell VSR4
* Schutt Air Advantage
* Schutt DNA Pro+
* Xenith X1, and
* Xenith X2.