This is not complex, at 2412Mhz (start of 2,4Ghz wlan) does not harm you at the transmission levels used in wireless network. The transmission power is around 100mW, based on the law of square that signal fades quickly when the distance is more then 100 meters. Just if there is nothing blocking the signal. If anything is blocking the signal it fades faster and more quickly. At 5180Mhz (start of 5Ghz wlan band) the signal goes even shorter distance at the same power.
The idea that people can get sick or even cancer from normal radio bands (2Mhz to 60Ghz) is just ridiculous. It is nothing more then a chance that this boy got the brain cancer. It has nothing to do with wireless networks, mobile phones or television transmission masts (they broadcast in the 230 to 800Mhz range). Mobile phones are in the range of 700Mhz to 2100Mhz (LTE/GSM/3G). Depending on country and location.
For the sake of discussion I have simplified use of frequency band used in mobile phones and 5Ghz wireless network.