Why does my dog do this?

Do you know those stuffing less dog toys like skunks and raccoons ? Well we got my dog a few for toys and anyway at first she was afraid of them but now she thinks they are her babies. She carries them around everywhere she goes (very gently), barks at anyone who touches them, licks and cleans them constantly, and i think she has even tried nursing this a few times. Do you know why this might be?