Four orphaned kittens, one female and three males, lost their mother just after they turned two months old. Since then, the reader reports that the kittens have been trying to suckle on one another, and separating them has not stopped the behavior.
Dr. Paola Cuevas (MVZ) says this is called non-nutritive suckling. She says it is not necessarily hunger at this age, and that it is a comfort behavior. She says research in orphaned kittens has documented cross-suckling between littermates, with a higher risk in kittens that lost their mother.
Dr. Cuevas suggests redirecting the behavior instead of only trying to stop it. She points to a purpose-designed kitten nursing surrogate, described as a soft plush object fitted with artificial nipples, or a very soft, durable, washable object made for this use. She advises against improvised items that could shed fibers, unravel, or be swallowed.
She also says some cats keep this habit into adulthood, directing it at blankets, clothing, plastics, themselves, other cats, or owners. She says it becomes a concern if a cat chews and swallows fabric or fur, or if another cat develops irritated or injured skin.
Dr. Cuevas advises watching the areas the kittens target.