Found some great ideas from veteran teachers on teaching adjectives, like these:
1) Find a bunch of hats around your house, and line them up. What words would your student use to describe each hat?
2) In the side of a small cardboard box, cut a hole large enough for your child's hand. Go in another room and place a "mystery object" inside the box. When you return, have the child place their hand in the box. What adjectives would they use to describe the object? Can they guess the noun in the box?
3) Here's a Grammar Rock video on Adjectives to help out.