The vagina is like a blind pouch or a tube sock. The cervix is at the deep end. It only has a tiny opening for blood and semen and the like. It is hard and not easily forced open. Tampons have not been shown to cause other damage to the vagina or cervix.
Infections are the only real concern.
Again, odor, discharge, pelvic pain, and fever are the general signs. Toxic Shock Syndrome is the most feared. More likely, a woman may get a bacterial vaginosis, which can be easily treated. Thoroughly wash your hands. This prevents introducing outside bacteria into the vagina.