Hi,
Having coached from under 11's to under 16's and played for over 15 years these are the things I would strongly recommend:
1 - Gum shield (don't skrimp on this, if you can afford a properly fitted 1 then do it!!!). Gum shields provide protection for more that just teeth, they can actually help prevent shock travelling through the teeth and causing other injuries.
2 - a Scrum Cap (or head gear). These are wrongly reffered to as scrum caps as believe me, whether you play in the forwards (in the scrum) or backs a kick / knee to the head hurts and can cause serious injury. It sounds to be like he is learning so more protection to the head area is very important.
Also, you may like to think about:
- Shoulder pads. They don't need to be massive (in fact there are rules about the size they can be, but if they are IRB approved they SHOULD be OK). Again, don't be fooled that these are only for forwards or pro's. They provide protection to one of the most used and vunerable areas of the body in rugby, no matter what position.
- I have seen people whear shinpads (especially in the front row of the scrum), however if he is out in the backs he probably won't need these.
I don't mean to make it all sound scary, but rugby is a physical game and taking sensible precautions against injury is, well, sensible. Last thing I would want is for a new player to give up because they got a preventable injury.