Hello, thank you for your question!
If you are talking about Reactin at a concentration of 5mg/5ml, and you give 10ml to your son, it is already the adult dose. You have to give the medication time to be fully effective, which is about 3 to 5 days
If, however, the product did not improve your son's symptoms, there are other anti-histamines that can be tried. I invite you to consult your pharmacist who will be able to suggest alternatives depending on the stock available
I also suggest the use of saline solutions such as Hydrasense or Sinus Rinse for nasal hygiene. Their use can greatly help to decrease mucus accumulation, and help to decrease symptoms such as coughing, congestion and sneezing. It can be used as often as needed. Also, I suggest changing clothes after your child gets home, and avoiding keeping the windows open in dry, windy weather.
I hope I have been helpful, I am available if you have any further questions!
Tom Samaha, Pharmacist