Every school district and private youth sports organization should have a sideline protocol for dealing with head injuries, and all sideline personnel should practice the procedure.  You don't want to have to think about what to do when facing a situation where time may not be on your side.

What to do if your athlete is hurt...
 
1) Remove the athlete from play immediately, and KEEP THEM OUT if any concussion symptoms are evident or if you suspect for any reason, that the athlete may have sustained a concussion.

2) Perform a sideline evaluation If you do not have access to an athletic trainer or other medical professional, assess the athlete using the Sideline Concussion Evaluation Tool or SCAT 2 and determine if emergency medical assistance is required.  If not, re-assess the athlete every 5-10 minutes for several hours after the injury.  Consider assigning a staff member to stay with the athlete at all times to look for signs of deterioration. 

3) Notify the athlete's parents that their child has suffered a possible concussion.  Make sure they know the
     signs/symptoms, and that their onset may be hours or days after the injury occurred.

4) Only allow the athlete to return-to-play if they have written medical authorization Have the athlete obtain a written return-to-play authorization from a qualified medical professional and ensure that they are 100% symptom-free at rest and during exertion (see below) before allowing them to resume practice or play.

5) Verify that the athlete is 100% symptom-free before allowing them to participate in any activity.  Coaches are
     sometimes the last to know.  Ask parents/teammates if they're aware of any lingering symptoms such as a headache.

6) Institute a gradual return-to-play procedure after the athlete is medically cleared, and make sure they are
     symptom-free during exertion.  If symptoms return during exercise, their brain may not be fully healed.

Related:   Guidelines for care of the unconscious athlete

The CDC's "Heads Up" campaign
offers free downladable information for:                 

            coaches                    schools

            parents                      athletes

Additional resources from the CDC