Temper, temper....

Where did my little angel go? Recently Michaela has been getting harder and harder to deal with. She gets her mind set on something and won't let it go.
Today while we were out getting Logan's shots done she noticed a bell on the Public Health Nurse's desk and the whole time we were there she demanded the bell. Then it turned to crying and shrieking and all out mayhem because we wouldn't give her the bell. I was at my wits end because today didn't start out good in the first place. I went to have a shower and Michaela came up with the salt shaker. I came downstairs to find that she had salted my entire Living room, dining room along with the chairs and the kitchen. I partially got that cleaned up as I would vacuum later, when she came up with her hands full of some kind of goop. I again came down to find that she had found a sample shampoo bottle and proceeded to pour it all over the living room floor and up the stairs. At this point I am getting angry. Then she told me that she was wet from her milk, which I discovered she poured all over one of the couch cushions. These mishaps happened between the hours of 10am to 11:30am. On top off all this I've had to deal with many temper tantrums and I am at a loss as to how to deal with it all.
Not only has Michaela been acting up, but Logan is too. His tantrums last a good 20-30 mins if not longer and it's not just one but 3-5 a day and I am having a hard time dealing with both of their tantrums. I just don't know what to do at times and I find myself loosing control far too often. I just hope that thigs get better from here because they certainly can't get any worse.
Any suggestions?