Wait... so this person is teaching it? Or the kid's parents? Or the other grandparents?
If I were going to teach chemistry to my grandkid, it would be different from trying to spark interest in chemistry. If I have grandkids someday, I'll be getting them toys like DNA/skeletal/atomic model manipulatives. My brother got a set of atom manipulatives once for school (disclaimer: I was homeschooled), and they're incredibly addicting to play with, even if you're not building molecules out of atoms and sticks. Watching videos about dropping gummy bears in potassium chloride or pouring thermite on computer hard drives helps, too.
But if I were going to teach homeschool chemistry, I'd make sure that I introduce physical science early in school (like, 9th grade), and consult my college chemistry textbook when teaching chemistry. This would be hard if you've never learned chemistry. Some homeschooling curriculums offer video courses, and some homeschool groups get together and go to an actual high school facility for these classes. I'd recommend this to anyone who hasn't had chemistry, but is faced with teaching it.