It looks like baby is milk treading it.
My guys do it on certain material. That toy looks like fleece, my guys LOVE fleece. Vienna will milk tread fleece before going to sleep on it.
Many people say they do it because kittens were taken away from their mother too early, but Butch milk treads me loads and he is one of Viennas kittens we kept. I dunno how much it has to do with being taken away from their mother.
Maybe it is a comfort thing?