Thank you for the added information. It helps a lot. I believe I can now be of help with this issue.
First, let me say I can imagine how worrisome this situation must be for you. You are clearly a loving and caring grandmom. And you're seeing your sweet grandson become a bit of a tyrant and that is indeed worrisome.
The key for me in understanding this came in your statement: he "has a 2 year old brother. They play at the same time but when they play "togerher" it is not a good thing. He encourages his brother to misbehave and they make all kinds of messes." That was very reassuring to me along with being able to rule out Asperger Syndrome. Why reassuring?
Because this is normal sibling rivalry behavior for smart 3-4 year olds. Get their kid brother in trouble! This is so common in one form or another and it helps us know how to proceed.
Your grandson is bright and fully capable, emotionally very aware and alive (good, now developmental problems like Aspergers). He seems like a great kid. Your son seems like everything developmentally checks out okay. That's important. Because his parents and you need to do two things: set limits effectively and let him be developmentally younger and safe again.
First, setting limits: this has gone on so long that I think your grandson has just gotten the idea that it is his right to be the dictator. What started out as a way to let out his developmental need to be a bit younger and let out his frustration at having to be good has now become a habitual pattern of behavior. And this makes it very tough to change. And changing will mean having to retrain him as to how to let out his frustration in acceptable ways. It is going to be a wholesale change for him and not easy for the adults. Let me give you the name of the classic book for doing this on your own before turning to a professional for help. This is really for older kids, but he's an only child and you're on your own and he's going to get older:
Setting Limits With Your Strong Willed Child by Robert MacKenzie.
Next, letting him be younger and safe again:
Remember: the problem started out because your grandson is bright and as a little guy is using up all his internal resources being good and following orders in preschool. And he has to be older and more competent than younger brother. And he has to be good and share his parents and grandmom. And he can't just be the center of things and a little baby like younger brother was able to and still can. He keeps upping the ante because he doesn't really know how to set limits for himself. When a little boy feels total developmental frustration, having punishment just becomes another way to express it. So it rarely works because he's used up all his resources anyways and cant' really control himself.
So, what to do?
Here is the clincher. He has to decompress. The world has to become safe for him to be a real little kid again. At home, he needs to be allowed to be developmentally younger. Even as young as his brother. If he has some favorite toys from 1, or more years ago, bring them out to play with him and see if he wants to. Don't push him, but let him be younger. He has a lot of kid development he's expected to excel in every day. So, let him be young. If it means playing cuddly games on your lap, fantastic! If it means singing songs he liked as a baby, great! At preschool, he has to contend with teachers' expectations that he does not really understand so well. So let him decompress at home. Let him be young and your little baby for a while longer.
Does that mean permissiveness? No. He has to follow rules that are age appropriate. And consequences. And you don't waiver from them. You must be consistent. He's too bright for inconsistent application of rules. You'll increase his anxiety. But outside of that, let him be a young as he would like. Let him know it's okay to be that young even though there's baby brother and he's the "big boy". But not with words: SHOW him it's okay by playing with him in young ways.
I hope you can feel my enjoyment of his smarts and my concern for his emotional development being allowed to relax and be little boy emotion again. And my trust in you conveying to his parents how to understand what I'm setting up as the plan here.
A great book for the long run: I want to recommend that you read a wonderful classic, How To Talk So Kids Will Listen & Listen So Kids Will Talk. It is from the 1980s by two therapists who studied with psychologist Haim Ginott. You can still find his wonderful books. If you want to go for the original, Ginott's book, Between Parent and Child, is still relevant and readable after all these decades.
They wrote a very famous book you can get if you like this one. This one is Siblings Without Rivalry: How to Help Your Children Live Together so You Can Live too by Faber and Mazlish.
I wish you the very best!
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