Mine just started doing that too.
To begin with - DO NOT RESPOND!
After the not responding, if it lasts longer than a few minutes I take her to her room, sit her on the floor, and tell her this behavior is unacceptable. Then I leave and by the time she gets up off of the floor and gets back to the living room she usually has forgotten what she was throwing the tantrum about.
If, when she comes back out she is still throwing a fit, usually that means (at least for her) that something is actually wrong, I figure out what it is and then feel like a terrible mom for not addressing it beforehand, lol (that happens maybe 1 out of 10 times. Its usually just a tantrum)
at 6:37 PM on May. 19, 2009