Its stated that The official age of use from Oculus/Facebook is 13 years old…. BUT this likely has to do with privacy and advertising to minors laws more than any other reason.
Dont get me wrong though the point is because of this reason there is not much content specifically for kids although he may enjoy the Star Wars titles. Warplanes, Space Pirates and it may also pay to take advantage of the educational stuff available like Apollo 11 HD which is quite stunning , National Geographic etc.
Try checking some titles out on YouTube so you yourself can see what they are 🙂