A tampon cannot cause damage or a miscarriage. If a little tampon could cause harm, pregnant woman couldn't have sex or use sex toys. I used plenty of tampons waiting for my period to come while I was pregnant and didn't know it.
I think you aren't supposed to use a tampon durring a m/c becasue the cervix is open and the rate of infection is higher. I don't think the tampon has any negitive effect to the baby, or would cause a m/c.
I can't imagine it would, because the tampon doesn't go all the way up by your cervix, at least it shouldn't. But you shouldn't use a tampon if you think your pregnant. Even if your having a m/c you should still not use a tampon.