Jessica Biel has written a children's book about menstruation that she hopes will encourage important conversations between kids and "their grownups," the actor has announced.

Biel's "A Kids Book About Periods" is a part of a powerful campaign started by Penguin Random House subsidiary DK to tackle sensitive topics about growing up and make them approachable for families and, most importantly, positive experiences for kids, DK wrote in a news release on Thursday.

To help de-stigmatize the topic of menstruation for young readers. Biel partnered with DK and PERIOD., a global youth-fueled nonprofit that works to end period poverty and stigma.

"People don't talk enough about periods," Biel said in a statement. "I’ve always felt strongly that we need to normalize the discussion around periods and as a parent, writing this book felt like an organic way to engage kids in the conversation from early on."

"A Kids Book About Periods" will be available nationwide on May 7, but is available for preorder now at Target and on Amazon, among others.

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Biel shares the news with fans, some react viscerally

Biel shared the news with her 14 million followers on Instagram Thursday, and some had feelings.

"If we grownups have the confidence to tell the truth about how menstruating bodies work, then we’ll give the kids around us the agency and voice to talk about their own bodies with confidence, now and for the rest of their lives.‼️" Biel wrote in her caption.

But comments started flooding in over the avoidance of the word "girl" in the book.

"She said a kids book because boys need to read this too," one commenter wrote. "Boys grow up to be men and men are generally partners for women. Boys need to understand more about women’s bodies so they know what they need to protect."

Many comments reiterated the fact that the distinction should be made by Biel. "Remember that only biological FEMALES can have periods. Period. End of story," one user wrote, but support continued to roll in over the launch of the book.

"Why is everyone so up in arms about not using the word girl?" another user commented. "I taught my 4-year-old son about periods so he can one day be a supportive partner or friend to someone with a period. I wish I had this book available when I did. Everyone should understand more about periods so that girls and women don’t have to feel shame or secrecy around it."

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Biel shares story of first period

A few days before announcing her book, Biel shared the story of her first period on Instagram as she was getting dressed for her day.

"I was so scared,” Biel said. “I locked myself in the bathroom. I was crying hysterically, I called my mom. I told her, you know, 'Something's wrong.' That's what I felt, I felt like something was wrong with me. Even though she had prepared me, I wasn't prepared."

She added: "I managed to do everything I needed to do that day and still have my period, so pass that around."

Biel − who shares sons Silas, 8, and Phineas, 3, with husband Justin Timberlake − hopes "A Kids Book About Periods" will be an important conversation starter that encourages better body awareness and positivity around menstruating, something she didn't have when young. And for Biel, it's just as important to share with her sons.

"Getting your period is actually pretty cool, it’s one of the things we share as human beings," she said.