Hello and welcome to Just Answer;
The vagina is a muscle that expands when something is inserted into it, such as a tampon, etc. It also expands during childbirth to allow the baby to be delivered. It then collapses after the object/ item is removed and stays this way unless something else is inserted into it. If the vagina seems 'looser than usual' which is more common after childbirth, it is helpful to do kegel exercises (squeezing as if you were trying to stop urine from passing) to help stregnthen the vaginal muscles.