Britney Spears' boys are all grown up.

And it's a concept that even the "Toxic" singer is having a hard time grasping. Days after sons Sean Preston and Jayden James turned 19 and 18, respectively, Britney—who shares her kids with ex-husband Kevin Federline—shared a message marking the milestone.

"This month is my boys’ birthdays," she wrote on Instagram Sept. 16, sharing throwback photos of herself and her kids when they were toddlers. "Happy Birthday babies and I hope you get all your wishes and more !!!"

Sean celebrated his birthday on Sept. 14, while his younger brother became a legal adult on Sept. 12.

But even though Sean and Jayden are now no longer considered minors in the eyes of the law, Britney is likely to continue her child support payments to Kevin, who is currently living with their sons in Hawaii.

"Child support jurisdiction continues until the minor child reaches the age of 18, or if upon their 18th birthday they have not yet graduated high school, it continues until they graduate high school," Kevin's attorney Mark Vincent Kaplan recently told People, "but in no event later than their 19th birthday."

As he explained, "The child support in this case for Jayden is being paid consistent with that law. His graduation for high school will be in November."

Sean and Jayden relocated to the Aloha State last year to "get away from the L.A. microscope," Kevin's lawyer previously said, though they still "have a desire" to stay connected with Britney.

As Jayden noted in a 2022 ITV documentary, living with his dad has become a "safe place" to "process all the emotional trauma" he and his brother endured growing up in the spotlight. 

"We've both been through so much pressure in the past," he shared, adding that there's a "high chance" that attention on the family will continue given his mom's very public persona.

Still, Jayden stressed that he has "no hate" toward the Grammy winner.

"I—100 percent—think it can be fixed," he said of their mother-son relationship, "but I think it's just going to take a lot of time and effort."

To see more of Britney and her boys over the years, keep reading.

"It's so crazy how time flies .... My boys are so big now!!!!" Britney wrote in a March 2021 Instagram post. "I know … I know … it's very hard for any mama especially a mama with boys seeing them grow up so fast !!!! Talk about enough to make you go to your knees ... GEEZ  !!!! I'm extremely lucky because my two babies are such gentleman and so kind that I must have done something right !!!! I haven't posted pictures of them for some time cause they're at the age where they want to express their own identities and I totally get it."

"Great time at Disneyland today .... but I don't remember ever getting that wet on splash mountain!!!" the "Stronger" star captioned an August 2019 Instagram photo series. "Geeez .... anyhow my boys are older now, so they don't like their picture taken ever... so I was thrilled today when they said SURE!!!!! Such a great place!!!!!"

Spears shared a video of arts and crafts time with her sons in 2018.

"Getting silly with my kids on our day off from tour!" the artist captioed the 2018 post.

"This was from our lil trip to see Aladdin," Spears captioned the 2018 photo. "What a great show!!!!"

"Love when we go to our favorite spot on Sundays," she wrote on Instagram in 2018. "The boys are bigger than me now!!!!!"

The family enjoyed a trip to London during Spears' Piece of Me Tour. 

The boys and their mom did a little surfing during their 2017 trip to Hawaii.

"Going for a walk with my son and the dog always does wonders for my mood..." she wrote in 2017.

The dynamic duo saw some aquatic creatures in Las Vegas in 2016.

Spears and her boys celebrated Thanksgiving with their family members, including her sister Jamie Lynn Spears.

"Happy gobble gobble!" the Grammy winner writes in 2015.

The "Oops...I Did It Again" star celebrated July 4, 2015 at the Happiest Place on Earth. 

The "Toxic" singer shared a picture of her enjoying "the mermaid life" in 2015.

Spears' boys are all grown up.

The artist's sons helped her hold up her surfboard at the 2015 Teen Choice Awards.

The terrific trio shared a sweet smile in this 2015 pic.

Look at these cuties!

The singer and her two boys went all out for Halloween 2014.

"I've got the two cutest boys in the world!" she captioned the 2013 pic. "I hope y'all are having as nice of a #mothersday as I am!"

The proud mama took her boys to see the Los Angeles premiere of Smurfs 2 in 2013.

The boys enjoyed a sweet treat with their mom at this 2013 game between the Los Angeles Dodgers and the San Diego Padres.

The singer took her sons to the Broadway production of The Lion King in 2011.