My child covers their ears because they dislike loud sounds. Is it okay to use earmuffs?

Yes, it's fine. Earmuffs are a useful tool for getting through hard sound environments, and they're not "spoiling" your child. The trick is to use them not all the time but only in tough situations, like sports days or shopping centers. To help your child get used to them, start with quiet sounds in a situation where they feel safe. If the panic is severe, consult an occupational therapist.