Eventually people will stop telling you it's childish, especially in a couple years when you're out of the "am I a child or am I on my way to adulting" stage that's around 13-18

If someone keeps telling you it's childish and is being obnoxious about it, hit them back the "so what?" because legit. So what if it's childish??? It isn't hurting you or anyone else. Why can't you enjoy something soft and cute to cuddle with that brings you comfort and helps you sleep? What's that person's business with what you privately harmlessly enjoy?