For a pulled or strained muscle use RICE: Rest, ice, compression, elevation. Apply ice, stretch. If he's not improved in 1-2 weeks take him to see his doctor. He can take Tylenol as needed as well

With soft tissue mobs, manual therapy, and other therapy modalities.

Specific exercises, analgesic cream and physical therapy

Icing, temp, reduce sports, and restrict neck range of motion for two weeks. Acupuncture works well for pulled muscle.

Dr. Li 

Firstly, he is a child. Good healing and hopefully it’s nothing serious. Have you had him checked out by a sports medicine doctor or physiatrist? Please make sure he gets a proper diagnosis. So, if it is only a strained muscle, the good news is he will heal quickly, ice massage even a neck brace will help, but this is only temporary. Physio stretches, etc. He is very young, but still err on the cautious side. Have him checked, then a more complete plan may be implemented. I personally do not give children chemical medicine. I prefer natural medicine. There are lots on the market. A cream I use is holistic and can be massaged into the area. I like blue by doterra. I have no affiliations with the company. I happen to use the cream and other oils with great success. I use this on myself and swear by it. It can be used on a child. Only natural ingredients.