I just googled about wifi health effects and found mixed reaction from people. So, could not come to the conclusion.
However, at present I think that Wifi is not safe for children. It has negative health effects. Affects brain, cell growth etc.
I had a bad experience, i went bed turning on mobile hotspot by mistake. In the morning I was not feeling good, my brain was not relaxed like other days. So I always keep my mobile phone away from bed. However, i am not sure whether it was due to wifi or mobile signal.