Here's a similar conversation from last month that may help: https://maddiespetforum.org/thread/kitten-sucking-on-his-belly/ .
You may also want to check out From Helpless Newborn , an article by Dr. Susan Krebsbach, DVM, on our website. There are two sections that include information about nonproductive sucking behavior. From "Potential Behavior Problems of Orphaned Kittens" section:
Another potential behavior problem of orphaned kittens is nonproductive sucking. This is when a kitten sucks on an object, person or littermate for soothing, non-nutritional purposes - much like a pacifier. Although nonproductive sucking is typically benign, it can cause injury to the object of the kitten's affection - physical harm to the person or littermate and destruction of belongings. In addition, the kitten may ingest something harmful. Often this behavior self-resolves before six to twelve months of age, but it may evolve into a displacement/compulsive behavior.
From "Recommendations to Prevent Behavioral Problems of Orphaned Kittens" section:
Kittens whose nonproductive sucking is excessive may benefit from an enriched environment with many items to suck or chew. Examples include rawhides soaked in water, cat grass, beef jerky, food stuffed toys and chewy or dry food. Furthermore, if the kitten shows a preference for a certain (and appropriate) item, reward her only when she sucks on that object. For example, if the kitten has a fancy for cotton, an old cotton towel can be given to her so that she will have an appropriate item to suck on. Then, when the kitten starts sucking on the person's skin or clothing, place her on the floor and give the kitten the old cotton towel to suck on. Or better yet, redirect the kitten to a completely different appropriate behavior, like playing with a pole toy. Never punish this behavior; it can be anxiety based and physical punishment only increases conflict - leading to more undesirable behaviors. In addition, it should not be encouraged through petting or other positive reinforcement.
#PetBehaviorandTraining