The movie’s on-screen stuffed animals looked quite real. Many thought they are simply very good computer animations, but that’s not actually the case.
In fact, people on set were using real-life stuffed animals and were moving them with puppeteers. The crew made real plushies which were digitally recreated down to the fibers. Then the visual effects studio Framestone took that footage and digitally enhanced it.
This includes the obvious removal of the puppeteers and the real stuffied from the screen and animating the gestures and mimics of the digital plushies. Of course in some places they had to fully animate the characters, using the plushies only as reference. The rough footage looks quite complex and that’s because it is.
It’s a whole science to animate realistic things, let alone stuffed animals. Disney though wanted Pooh and his plush friends to look and feel as realistic as possible on the screen. Hence, the complex movie. But next time you rewatch “Christopher Robin” again, remember that Pooh was really there, along with his buddies.