My son Dallas will be four in June. His little sister Melanie is one and they were the best of fiends. About a month ago he started to be mean to her. Real mean. They dont have the same dad and his father left for Florida. When she returns from being alone with her dad he gets mean. He hits her, punches her, and just started to kick. I dont know if anyone else has had this problem but any info would be helpful. Thank you!