When dd was 4.5 she had a pet kitten that suddenly died. She asked for a new pet, something small and furry, and when we finally agreed she told us she wanted a tarantula.
Anansi has been with us for a year and a half now and he's the most fascinating pet. I love him! I wasn't keen on a tarantula at first either, but wow, he really is cool.
Endearing? Absolutely!
The good stuff: he makes no noise, he doesn't smell, the molting process is fascinating, you only have to change his bedding maybe 2x a year, his food costs about 50 cents a month, he's actually cute and interesting.
the bad stuff: you can't cuddle him, the crickets can be stinky and annoying, they are actually very delicate
Rose hairs (like anansi) are very calm, docile, slow moving... they certainly aren't escape artists or aggressive. They are kind of like a pet plant.

If you can trust your ds not to bother the tarantula (holding him etc) I think they are a perfect pet.
They can bite if they feel threatened, their bite has been compared to a bee sting. It's never happened to us. We hold Anansi rarely, but he seems really OK with it when we do. Mostly we just put our hand in the tank and let him decide if he wants to climb on. The main reason I would caution against handling a tarantula is because they are very delicate - even a drop from just a few inches can kill them.
I've read that one way to pick out a docile tarantula is to make sure the butt is furry. An angry tarantula flicks irritating hairs off his butt, so if the butt is bald you know he gets angry easily.