I had a similar problem with my RB Meezer Ming. He was a goof that loved everybody, until one day a friend and her daughter (about 10 yrs old at the time), came to the house. It was a very hot day and the a.c. was down for repair, and the little girl just wouldn't leave the cat alone, even tho he tried nicely to get away from her. I asked her not to pester him since it was hot and he didn't like the heat, but she kept at it, until finally Ming lashed out at her. From that day on, he had no tolerance for any kids being in his house (other than my own), and just the sight of another kid being around was enough to set him off. He would crouch, lay those ears flat, swish the tail, and literally scream at them. He remained that way for the rest of his long life. He was still a goof and loved everybody tho - just not kids.