Should I call child protective services?

The couple is in their late 20's with a three year old child. The dad goes off to work every weekday, the mom says she goes to school two days and two nights a week. The apartment is so nasty that I have seen maggots in the food on the dishes in the sink. They don't clean up anything. The bathtub is so icky I wouldn't stand in it with shoes on and they bathe the child in it! They meet the grandmother in the front yard and won't let her in the house for fear she will call the police (they've done it before). Recently, the little girl has been acting unreasonably afraid of her mother. She screams hysterically if her grandmother tries to drop her off if the dad isn't home. One time when she came home and the dad was there and the mom's car was gone I HEARD her say, "It's ok, it's ok, she's not here, she's not here," to her grandma. I have seen no evidence of drug abuse, spousal abuse or physical child abuse, just the nagging feeling that something is not right with this situation. If you add that to the downright filth they are living in, does it equal a call to DFACS or Child Protective Services? What do you think?