My mommy hat is all askew. Help!

My kids are driving me insane.

Surprisingly, the youngest one, who's twenty months old, is causing me the most grief. She throws fits almost every day--screaming at the top of her lungs, lying on the floor and kicking, running away from me--and almost always in public places. Today it was the library. She had a tantrum because I said it was time to go, and it felt like every eye in the place was on me, watching to see how I would handle her. I could feel the disapproval, particularly from an older lady who was standing near the new fiction and looking at me with that "Can't you control your child" face. I wanted to tell her off, believe me. She can't tell me that her children (if she has any) didn't pitch fits at the most inopportune times--unless her kids were perfect angels, which I suppose in her mind they were.

My four-year-old has his share of tantrums as well, but he's never been as willful as my daughter, even when he was her age. His fits consist mostly of screaming loudly enough to alert people within a mile radius, then sobbing like I've just told him that the Easter Bunny ran out of chocolate eggs. These tantrums are embarrassing, for sure, and really, I'm at the end of my rope.

So I'm begging you as one harried mom to another: how can I stop these tantrums--or at least regain control of my kids? Help!