What camera is better for a child?

I want to buy a Fuji Instax 210 for my 9 year old sister as a gift in a couple of weeks. But I know it's pretty big and she's very tiny for her age lol. Which is why I'm

I really don't think you should be overly worried about the 210 being too big for her. It's not heavy or difficult for small hands to operate because it's very simple. On that note however, I highly doubt that a 9 year old is going to complain that the images from an Instax Mini are too small! If you think she would prefer the 8 due to the size and colours, I wouldn't think twice about it. She is not looking for optimal image quality.
My daughter is 2 years old and loves instant film. She has dropped our 7s a couple times and it keeps shooting fine. She's not to handle my 90 without supervision but she loves that too! Kids love and are fascinated by instant film. Please don't be discouraged by those who suggest digital or disposable cameras. 9 is a great time to shoot instant film. She's old enough to choose reasonable things to take photos of at the right time and certainly this will teach her how to handle delicate electronics. As if a 9 year old today doesn't already use iPhones etc anyway!
Anyway, I think she'll enjoy whatever instant camera you choose! And if she doesn't you can always return/exchange it. No bid deal.

My experience with cameras and 9 year olds, is that it is a very fleeting relationship. As long as your are willing to accept that, get the larger one. She will be able to handle it, with the proper instructions.

How do you know it is "big"
Take your daughter into a shop that sells Fujifilm Instax cameras and let her try them on for size.

Keep to one of the small, cheap, one-time use pocket cameras you find at CVS or Wallgreens. They sell for under $10. Then if she looses it or drops it, no one will get upset. Give her the chance to take pictures without it being complicated. At age 9, just let her have fun with it.

Waterproof, crushproof, shockproof, dustproof, sandproof, mudproof digital camera?
Gave my son a dSLR when he was 11.

Not a bad choice---Would highly recommend you purchase it ( preferably the Mini 7S ) via adorama.com [ Free shipping!) Hope this helps