I have a 13 yr old son who has always been a bit of a whinger and moaner. He is the type to moan about doing something before he does it, but once he does it he is happy and positive. The exact same situation can create the same reaction next time.
For example my son goes to martial arts class one night a week. He always moans that he doesn't want to go, says he doesn't like it, that he's no good at it, that he would rather do something else. However, when I collect him, he is full of smiles and positivity, chatting with the friends he has made there and being full of beans.
He has been like this with EVERY club he has ever been to. The only time I have actually stopped him from going was when he started to come away from the club being negative, then I know he isn't really enjoying it.
The way I have always dealt with it is to acknowledge how he feels, tell him that he will enjoy it when he gets there and then just ignore the moaning. I talk about other things and refuse to get drawn into a long debate.
My partner (not my sons Dad) got really cross with him this week and said that he is miserable and negative, unenthusiastic etc. I have always said to my partner that I don't particularly like the negativity in my son, but I don't see I can do much about it apart from not pander to it.
My son gets very enthusiastic (almost obsessional) about new things, so it's not like he's melancholic all the time, he can be very happy and in lots of ways is placid and easygoing.
I suppose I am just posting to see if you think my approach is right as my partner makes me feel I am doing something wrong. 