I have an 18 mo old and she has a pillow in her crib. She has asthma and gets colds pretty frequently so we got her one to elevate her and help with the cough. She doesn't stay on it all night, but she uses it part of the time. So obviously I don't see a problem with it. It's been in there for about a month now and it's not been an issue.
My 18 mo sleeps with stuffed animals in his crib. It provides him comfort and helps him sleep better. I think this might be a child to child thing. I think it really depends on what your comfortable with.
DS has a Aden and Anais swaddle blanket and this puppy that my MIL gave him, no pillow yet. He is always cuddling with this and has satin on the opposite side.
Re: 18 Month Old and a Boppy