I sometimes hear people using us, we etc. when talking to young children in order to refer to the child: e.g "Let's get our socks on"; "Aren't we a clever boy". For how long have people done this? Is this as common as I think it is? And does it occur in other languages?
As a point of possible interest I might add that in Antony & Cleopatra (about 1607), when Cleopatra is helping to lift up the dying Antony on to her monument, she uses we/our in a way that might be interpreted as resembling this usage:
[...] but come, come Anthony,
Helpe me my women, we must draw thee up:
Assist good Friends.
Oh quicke, or I am gone.
Heere's sport indeede: How heauy weighes my Lord?
Our strength is all gone into heauinesse,
That makes the waight.
Of course this could just as easily refer to both of them, although it seems to have some relation to the 'hedging' described in Edwin Ashworth's comment.