I think I know what you mean, but I would avoid anything that isn't sufficiently glazed. I've seen plaster statues and such, and it's just straight plaster with paint on it, definitely not safe or at least I wouldn't risk it. Plastics are perfectly fine, as well as ceramic, but I would avoid plaster. You're better off finding some nice big stores, washing them, letting them dry and setting them up in there, they'd probably like that better than a big, googly eye creature or something staring at them.