This does the rounds every year or so.
In the UK there was never any problem with it under the previous rule sets and also there was caa guidance to do with dealing with airsickness and the safety pilot courses which even promoted the giving controls to a none qualified pax on private flights.
Now a lot of EU countries it wasn't the done thing using exactly the same JAR regs as the UK used.
Under EASA I don't have a clue. But to me getting a pax to fly the plane S&L while the pilot gets the NAV sorted is good airmanship.
But.. its very hard for anyone to find out and also to prove post event. So as long as your mate doesn't go and publish nobody will really know.
Letting them landing and takeoff wouldn't be a good idea or for that matter flying at a level which would cause issues with an engine failure.
There are hundreds of pilots every year let there kids fly the plane under proper supervision with no major accidents.