Many riddles are based on word puns and can be an interesting means to help with expanding a child's vocabulary.

A riddle a day can be a great conversation starter between parent and child.

Here is a free list of riddles: Purple Kitty website - riddles

Some are more clever than others... some are corny... others may use archaic language.

ETA:
- More vocabulary-building resources in this old post.
- Discussion of vocabulary deficit in this old post.
- Expanding vocabulary as part of an enriched home environment, found in resources in this old post
- Adult vocabulary skills mentioned in this old post, and in this old post (hat tip to philly103).