Our youngest cat was given a fluffly blanket when he was a kitten and almost straight away started suckling on it, as well as kneading it with his paws to try and get (some more) milk out of it.
I have seen poddy calves doing the same thing, except they suck each others ears!
He did this for about a year or so, but we never found it anything to worry about; we just assumed it was a mammal reflex thing and that it had become a comfort action for him.
Maybe you could find a similar substitute for your little guys?
He still has the blanket but he only sleeps on it these days, and is a perfectly normal little demon spawn monster cat.
Cheers,
