This post originally appeared on The Huffington Post.

Here at Safe Kids, we often hear from parents who have faced the heartbreaking loss of a child. You will want to read this story by Gordon and Julie Ross, loving parents who are eager to share their story so other parents can learn from their tragedy.

-Torine Creppy, Chief Program Officer for the United States

This week, 49 children and staff from Finch Elementary School in Atlanta, Georgia were taken to the hospital for carbon monoxide poisoning.

As a certified child passenger technician and instructor, working in injury prevention, I frequently hear this question. Not surprising, given tight household budgets and the constantly increasing costs of raising children.

First, let’s look at the things that rule out using secondhand seats, then we can better determine when it’s okay.