Headache is common. Concussion is a change in brain function that occurs after head trauma. There does not have to be loss of consciousness. Symptoms include headache, confusion, dizziness, nausea, sensitivity to light and memory problems. If a concussion is suspected the child should be removed from play. Evaluation by a medical professional to make sure they are symptom free before return to play is crucial.
Can vary. Childhood concussions can be a bit different from adult concussions in that sometimes a child will simply stp speaking for a brief or longer period, but certainly loss of consciousness of varying lengths, headaches, dizziness, amnesia, vomiting, nausea etc. Are signs. See http://cpancf.Com/articles_files/childhoodsportsconcussions.Asp.