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Concerned Aunt was started.
It would involve too much speculation to comment on what might be generating your nephew's behavior. It would be wise to arrange an evaluation by a pediatric behavioral health clinician, and part of the evaluation will be a consideration of the overall family situation. From a behavior management perspective, you can gain some helpful guidance by taking a look at Lynn Clark's book SOS Help for Parents. You and your sister will find it to be a reliable guide for managing common childhood behavior issues, not only with the three-year-old, but with all the children.
I have a 4 year old nephew who sounds the exact same only difference is his parents split when he was a baby, although he still see's his dad.
I agree with the comment above i think the divorce has a lot to do with the tantrums. Kids pick up on emotions from their parents really quickly and they tend to play the parents off each other which will make things even worse if they don't come to some sort of agreement.
Stick in there it might sound extreme at the moment but with some quality time and patience with the boy things will slowly begin to turnaround.
i think that the divorce maybe affecting her daughter emotionally because of the negative vibrations surrounding her.
i mean i may be wrong. but iam quite spiritual and i do believe that because children at that age are still developing we should be more positive around them so as to send POSITIVE vibrations to them instead of negative. although your sister may not know that this is happening.
i dont know what else to say as iam only 16 myself & looking to become a child pyschologist. so if you do have any queries on this topid please do not hesitate to contact me at my email chanz--***@****.
hope this has helped.