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Since, in verbal speech, there's is often misused, it's okay in dialogue.

It's also okay to use there's if a proceeds the plural noun:

There's a lot of grammar terms that are difficult to remember.

There are lots of grammar terms that are difficult to remember.

 

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My high school writing teacher did the very same thing. I once described a "big mountain" in a short story. He circled the phrase in red and gave me an "F" until I changed it. I revised it to "the pinnacle kissed the gates of heaven." He liked that a lot better.

A child in a story would look at a big mountain, not a pinnacle that kissed the gates of heaven. It's all about what is appropriate and what isn't.