Britney Spears says it's 'bittersweet' seeing sons Sean, 16, and Jayden, 15, ...

Britney Spears says it's 'bittersweet' seeing sons Sean, 16, and Jayden, 15, ...
Britney Spears says it's 'bittersweet' seeing sons Sean, 16, and Jayden, 15, ...

She shares two teenage sons with her ex-husband Kevin Federline.

But Britney Spears was having trouble accepting that her boys are becoming young men in a sweet Instagram post she shared on Friday.

The 39-year-old pop icon was pictured on various trips to the beach with her young boys in the vintage photos as she bemoaned how 'bittersweet' it was to see them growing up.

Memories: Britney Spears, 39, posted throwback photos to Instagram on Friday showing her sons Sean, 16, and Jayden, 15, when they were young boys

Memories: Britney Spears, 39, posted throwback photos to Instagram on Friday showing her sons Sean, 16, and Jayden, 15, when they were young boys

In one of the photos, Britney was seen carrying one of the boys while she wore a floral-print bikini with a backwards baseball cap and dark sunglasses.

Sean and Jayden were also pictured running together by the edge of the water, and the singer helped to dry one of them off with a towel in a third snap. 

'So bittersweet to see them get older … why can’t they just stay babies forever???' she wrote in her caption, adding, 'They will always be MINE!!!!!'

Although Britney shared pictures of her sons from when she was still a young mother, her fans recently got a glimpse of how much they've changed.

They grow up so fast: Britney wrote that it was 'bittersweet' seeing her boys grow up. 'Why can't they just stay babies forever???'

They grow up so fast: Britney wrote that it was 'bittersweet' seeing her boys grow up. 'Why can't they just stay babies forever???'

Beach day: The boys were pictured during a beach outing with their mother; pictured together a few years later

Beach day: The boys were pictured during a beach outing with their mother; pictured together a few years later

All grown up! Earlier this month, the singer's seldom-seen sons were pictured in photos posted to Instagram by their father Kevin Federline's friend, who also shared images of Kevin relaxing

All grown up! Earlier this month, the singer's seldom-seen sons were pictured in photos posted to Instagram by their father Kevin Federline's friend, who also shared images of Kevin relaxing 

Mature: Sean (L) sported a thick mass of curly hair and wore a simple black hoodie with dark jeans, while Jayden (R) wore his dark hair shaggy and had on a black sweatshirt with yellow-dyed pants

Mature: Sean (L) sported a thick mass of curly hair and wore a simple black hoodie with dark jeans, while Jayden (R) wore his dark hair shaggy and had on a black sweatshirt with yellow-dyed pants

Earlier this month, the singer's seldom-seen sons were pictured in photos posted to Instagram by their father friend Eddie Morales, who also shared images of Kevin relaxing. 

Sean sported a thick mass of curly hair and wore a simple black hoodie with dark jeans, while Jayden wore his dark hair shaggy and had on a black sweatshirt with yellow-dyed pants. 

Morales seemed to turn to Kevin and his sons as inspiration while dealing with a loss. He wrote:

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