When Phil Ferguson told his daughter he was an atheist, she didn't seem to care. 

But his son cried for 24 hours. 

That's when he knew he'd let the church get to his kids too much. 

"The churches know they have to get to the kids," he said. 

Ferguson grew up Methodist, but eventually left the church and became an atheist. When he and his wife had children, things started to shift – a little. They had their children baptized and later enrolled them in the Christian pre-school, followed by Christian elementary school. Ferguson spent three years on the Christian school board. All the while, he was "a closeted atheist." 

By the time he decided to be open about his atheism again, his children were alread steeped in Christianity – the reason his son cried so much is because he thought his dad would not be in Heaven when he died. 

That, in part, is why Ferguson sees the importance of being open with children about atheism. 

The other reason? According to data the Pew Forum on Religion and Public life released in October, the number of people who are religiously unaffiliated is increasing – about one in five Americans falls into that category.

The younger the age demographic, the higher the percentage of unafilliated people, also called "nones." Among those 65 and older, only one in ten people claims no affiliation. But in the under-30 crowd, about one third of adults are unaffiliated, according to the Pew data. 

Being unafilliated does not mean someone is atheist, or an agnostic (*one who believes it is unknowable whether God exists). Atheists are just part of the unaffiliated. But that atheist niche is growing. 

"Some people don't think it's a battle. I do," he said. "We're winning the battle." 

Still, he cautioned his audience: "Do not underestimate the power of religion to get kids."

Here are some of the tips he offered his audience for talking about atheism with children: 

Be open. Some of the neighbor children new Ferguson was atheist, and when they said something about it, he told them more. 

Have fun with science. He recommended stevespanglerscience.com. 

Give children books about evolution, science, etc.

Listen to talks. When Ferguson played a talk by Julia Sweeney with his children in the car, they heard it and got more understanding of atheism.  

Do magic tricks – and optical illusions, too. "Things are not always what they appear to be," Ferguson said. 

Show Youtube videos, such as those The Thinking Atheist and Dark Matter 2525, and the Mr. Deity series.

Introduce them to atheist musicians, such as George Hrab.

Teach them about different world religions.

*CORRECTION: This story has been updated to include a more accurate description of agnosticism, in response to the reader comments below.