mine very whingy at the mo too. Am putting it down to the weather (she hopes). I tell him I can't understand him unless he speaks nicely which works until the next time he wants something then it's back to whining again
Sometimes I whinge back but out-whinge her - it makes her laugh and helps us both chill out a bit.
The only thing that has really worked for us is me being more disciplined with undivided attention for her. So I tell her that we'll play for an allotted period of time and then I make sure she gets all of me for that time. No phone, no web, no little chores in between and I try to ignore the baby if I can. I give her a 5 min count down to the end of the playtime and then I ask her to allow me to do whatever I need to do and entertain herself. As she has come to learn that I really will play and she trusts me to do so, she's much better about not whinging at me at other times.
But - jeepers - some of her games are mind-numbingly tedious.
i just get grumpy and say if you keep on whinging then you wont get/do x nice thing i had planned for them to get/do that day. i am prob too strict but whinging drives me potty so i have to put a stop to it. i do carry through (or have one in the past) so it mostly works now. also is usually for me coz too tired/hungry so i try to do someting about that if i poss can....(dd1 is 3.9)
Mine went through this too at around the same age. Like the others have said i used to say " i'm sorry, but i can't understand you when you talk like that". It did eventually pass. Just don't rise to the whining as that way they have your undivided attention!!!