Busy Bones is a terrific site from Arizona State University. You'll find a virtual lab where you can dissect bones, a virtual bone microscope, bone experiments you can try out, and a complete skeleton viewer. You can even find out how bones fracture and heal, and learn from a forensic scientist about how bones can help solve mysteries.
At Wonderopolis, find out about the bones in your body, how those bones grow, and how cartilage is different from bone.
Learn all about bones at KidsHealth, and watch a video about bones' different jobs.