Yep, they're no-neck monsters, all no-neck people are monsters
Maggie cattily dubs Gooper and Mae's brood a bunch of "no-necked monsters" at the beginning of Act I. The children in Cat are indeed monstrous, continually invading the scene. Against the beautiful, childless, tragic couple, the image of the family appears hilariously grotesque. For example, Mae and Gooper have spawned a litter of beasts fit for the county fair; and Mae is a "monster of fertility." This side of the family offers up a burlesque of familial love and devotion. Note in particular Daddy's birthday party in Act II.