Terrible 2's at 9 months?

I think Tori must learn from Andrew. That's the only conclusion I can come up with. Today has been worse than usual with both of them and every time HE cries, she starts up some water works of her own! The reason I think she is learning from him is because her tantrums (and, yes, they ARE tantrums) are identical--IDENTICAL--to Andrew's. Every little bit of it! She starts with a whine and then stomps her feet or hits the ground with her hand and then checks to see what kind of reaction she's getting. If I don't respond with a swift swat on the hiney, she'll jump in with the screaming and crying and kicking. It's so strange to see because Andrew never did that at 9 months old. It's actually pretty comical because she's so little (I know she's not LITTLE because she's so tubby, but you get the idea--she's not 2).

Any ideas on how to deal with this one? It's new to me. Andrew spoiled us because he was fairly easy going as a baby. Busy and into everything, but easy going.