My son (almost 4 yrs old) hit his head on a toy, right below the eyebrow 10 hours ago. i applied ice and comfort, he seemed fine and woke up with a small bruise, to be expected. but now he has developed a low grade fever, im not too concerned at the moment, its 38*c. i usually let fevers run their course unless they get over 39 just a little worried this might be something to do with hitting his head. should i take him to the hospital?