Ahhh..the terrible three's!! Makes the two's look normal, huh? LOL! He's testing his boundaries and you. As Tammy mentioned, changes affect little ones. With them not being able to fully comprehend, they get frustrated. Can you imagine not being able to communicate your feelings and thoughts to the people around you? Well, that's HIM!! Welcome to his world! LOL! Just set firm house rules and stick to them. It's gonna be hard to be consistant. It's always easier to just give in and give them what they want, but don't do it. One rule I have always had in my house that no one gets by with is: "You don't hate people. You can hate things, not people." All my kids grew up with that one. LOL! An important thing for you to do here is to STAY CALM!! No matter what! When you get visibly upset, he knows it and in his little mind.....he wins. Try saying to him, "I'm the mommie." put emphasis on "I'M". Tammy hit it on the nose when she said to spend one on one with him. Another thing that works well is: when he's being good at anything, acknowledge it. Even if it's just walking by and rubbing his little head with a smile. Saying "I love you" for no apparent reason helps too. He probably feels like he has to compete with your 3 month old. Let's face it, babies get LOTS of attention. And with everything else going on, he probably feels like he got lost in the shuffle. This is all normal. Sometimes, just stating in a firm voice what he's to do and sticking by it, no matter what, is enough. Try to make the punishment fit the crime. IE: taking his toys from him when he says "I hate you." will not connect in his little head. Having him say "I'm sorry." and giving that person a hug will bring the crime/punishment together for him. Remember to keep it simple for him. He is only three. Long explainations will go in one ear and out the other. Make simple statements and follow through. And when you say "No." make it stick. No matter what! Just keep saying in a calm voice, "I said No." Repetition is how they learn. Try not to pull your hair out over this, there'll be plenty of time for that when he reaches the teen years! LOL!!! In the meantime....enjoy the quiet moments!!
I'll be praying for strength and peace for you!!