I think a child would quickly get bored of a tortoise
Good point.
Alot would depend on the age of the child and whether or not her interest in a tortise was aquired because she was shown one or because it's a legetimate interest. When my daughter was little she wanted a pet elephant because she saw a man walking around with one in the village where we lived. Her interest will vary over time and she should pick a pet thats handleable for a child to help hold her interest.