Exclude Child Posts from WP_Query

How can I exclude child posts using wp_query? Given the following architecture:

• parent 1
  • child 1
  • child 2
• parent 2
  • child 3
  • child 4

I’d like to only return parent 1 and parent 2, and exclude child 1, 2, 3 and 4.

I’ve searched high and low for an answer to this question. Nothing surfaces.