"I have a fundamental rule that I will never lie to them, which is challenging at times," Dax Shepard said of daughters Delta, 3½, and Lincoln, 5½
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Dax Shepard and Kristen Bell have a big rule when it comes to their daughters: Don’t lie.

Case in point? The actors and parents to Delta, 4 this month, and Lincoln, 5½, are all about celebrating Christmas and the idea of Santa Claus with their girls, but when they ask about the validity of his existence, the stars give it to them straight.

“I have a fundamental rule that I will never lie to them, which is challenging at times,” Shepard, 43, told Us Weekly Monday during his visit to Children’s Hospital Los Angeles, admitting the “controversial” nature of the decision before explaining his reasoning.

Dax Shepard Joins Amazon in Delivering Smiles this Holiday Season
Credit: Michael Simon/Startraks

“Our 5-year-old started asking questions like, ‘Well, this doesn’t make sense, and that doesn’t make sense,’ ” recalled the former Parenthood star. “I’m like, ‘You know what? This is just a fun thing we pretend while it’s Christmas.’ ”

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Premiere Of STX Entertainment's "A Bad Moms Christmas" - Red Carpet
Dax Shepard and Kristen Bell
| Credit: Rich Fury/Getty
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Kristen Bell, Dax Shepard and daughter Lincoln
| Credit: Kristen Bell/Instagram

That doesn’t mean the girls don’t appreciate St. Nick, though. As Shepard explained to Us, “They love watching movies about Santa, they love talking about Santa. They don’t think he exists, but they’re super happy and everything’s fine.”

And just like the season’s most recognizable icon, Delta and Lincoln — who are newly “infatuated” with Barbie dolls, according to their dad — are learning all about giving not only at Christmastime but throughout the year.

“We encourage them to give something of theirs to whatever friend comes over,” Shepard shared. “We’re trying to show that an object can give you some joy when you get it, but then seeing how it can make someone else happy is sometimes even more fun than the thing was itself.”

https://twitter.com/daxshepard/status/415932233745068032Dax Shepard/Twitter
Dax Shepard and Kristen Bell
| Credit: Dax Shepard/Twitter

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Shepard’s comments about honesty when it comes to communicating with his kids echo the policy he and Bell, 38, have about discussing difficult topics with them — like death.

“I think giving them the tools to understand that certain things happen at a young age is important,” The Good Place actress said on WTF with Marc Maronin September. “We’re not morbid about it. We don’t talk about death, but she asks, we tell her.”

She also told Maron about why she doesn’t want her kids to have a religious understanding of death, explaining, “As a parent, in my life, what I really want to give to my kids is the science of it and the critical thinking of it.”