Stephanie, my son, who is now 15, started at age 3 using Fuji Quicksnap single-use cameras. He got really good with them, used the flash when needed, etc. all by himself and his compositions were GOOD. Got expensive after a while, so for his fourth birthday, I got him a Canon Sure Shot Owl. Its a simple autofocus point-n-shoot 35mm with a very large viewfinder that is easy for kids to see through, and it is super easy to use. I'd look for one of those. They're inexpensive, durable, and good...and easy for a little one to learn.
My son now shoots with a digital SLR. I know, I know....but he is not an artist like me, he is a computer geek who has taught himself two programming languages and who loves building with Lego. He shoots digital because me takes pictures of his Lego projects and posts them on Lego enthusiast websites. He shoots with an SLR with a 50mm macros lens, and he uses it all manual.
I shot this of him when he was four.