My Bernina dealer ( I work there 1 day a week) has the Bernette Sew Pink machine on special. One woman has bought 2 of them and is taking the classes with her granddaughter, who is 8. The granddaughter does not know that she will receive one of them for Christmas. The 8 year old had been loving the classes, and they want to continue to come on for sewing classes after they finish the machine mastery classes. She is going to start with a t-shirt, then pajama pants. This girl loves the machine, and since it's not a toy, she can grow into it.
The other one I would recommend is find one (or 2) of the older (70s) Kenmore 3/4 size machines that come in a rose-embossed clamshell case. They would be model #s 158-1030/1040/1050/1060. I had one I sold to my former boss for her 11 year old daughter who was in 4H sewing. That is a great kids machine and well built.