sound like a form of "sibling rivalry" to me too...

my 3yr old dcg acted out when the new baby 8mos old started care here...typical crying out for attention situation. I made sure to encourage her to be part of the babies routine. Like asking her which toys does she thing baby would want to play with or what blanket should we use. I would even say "hummm....baby is crying, I wonder what we can give her to suck on that will make her feel better" dcg with wide eyes would run and get the paci and she felt like SHE was the best helper ever. Oh and when baby was sleeping I made sure to spend some one-on-one time with 3yr old to make her know I'm still here for her.

Good Luck!