I have a son who's almost 2.5 and a daughter who's 6 months. We escaped jealousy up until now, but it's hit us hard lately. Every time the baby is playing with a toy, my son wants to take it away. All along we've been doing the "trade" concept, where if he wants to play with a toy, he needs to give the baby a different one. But it's not working anymore. He doesn't want to give her a different toy. And he doesn't even want to play with the toys he's taking - he just wants to put them away so she can't have them. It doesn't matter if she has one of his favorite things or something very babyish that he never uses on his own.
Of course, we tell him he can't do this, and he screams and tantrums and keeps trying to do it. I'm struggling a bit with how to come up with appropriate rules and consequences around this behavior.