The 18th birthday present Reese Witherspoon gave her daughter that didn't cost a cent.

18th birthdays are a big deal for parents. Arguably more so than for the newly minted adult themselves.

They’re an opportunity to reflect on the fully formed human you created, and post embarrassingly soppy photos on Facebook from when they were born or running around the backyard naked.

This weekend, Oscar-winning actor, Reese Withersoon found herself doing just that, with her daughter Ava hitting the big milestone.

To celebrate her first child’s coming of age, the 41-year-old came up with a beautiful idea to mark the occasion.

And it didn’t cost a cent.

Posting a photo of a stack of handwritten letters tied up in pink ribbon to Instagram, Ava shared just how much the simple gesture from her mum meant to her.

18 letters that made me cry (hard) today, courtesy of my lovely mother.

A post shared by Ava Phillippe (@avaphillippe) on Sep 9, 2017 at 9:37am PDT

“18 letters that made me cry (hard) today, courtesy of my lovely mother,” Ava wrote to her 446,000 followers.

Penning a letter for each year of her daughter’s life, Reese’s gift is a great idea for any parents struggling to sum up 18 years worth of priceless moments.

It just goes to show, often the most meaningful gifts are simple, sentimental and full of heart.

Ava is Reese’s first child with her ex-husband and fellow actor, Ryan Phillippe. The Big Little Lies star also has a 13-year-old son, Deacon with Phillippe, and a four-year-old son, Tennessee with her current husband, Jim Toth.

For more imperfect parenting advice, check out the latest episode of Mamamia’s parenting podcast,  This Glorious Mess…

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