Since 2010, concussions have been an increasing problems for kids per the Health of America Report. A 71% increase in related to "rough-sports-related concussions" to be exact. This was tracked by Blue Cross Blue Shield through medical claims for kids aged 10-19 years old, the age range that experiences the most concussions by far. Boys were twice as likely as girls to experience concussion, but of course they can happen to anyone.
This increase in concussions was so steep that Washington state enacted a "Shake It Off Law" in 2009 that requires medical clearance of young athletes before they can return to play after head trauma. The increase in awareness of this issue is important to prevent cases of far more serious paralysis, long-term memory loss and other long-lasting effects up to and including death. For parents it's important to be aware of your child's experiences on the field, and perhaps elsewhere (I had a child who received a concussion in Drama class, for instance).
Once a concussion is suspected, take proactive steps to have the concussion positively diagnosed by your physician, and follow medical guidelines for complete brain rest away from screens and books and school until no symptoms remain. It can be hard to wait out this recovery time, but it's absolutely essential for your child's brain health. When in doubt, sit it out.