It's not unusual to discover a sea treasure that washed ashore laying on top of warm sand.
It could be a message in a bottle, a lost locket or in this family's case, a large buoy covered in barnacles.
While swimming at a local beach in the small seaside town of Burry Port, Wales, the Gravell family spotted the "absolutely fascinating" object.
When 6-year-old Erin and 4-year-old Ellis asked their parents if they could touch it, they said, "sure."
"We didn't take much notice of the buoy," the kids' mom, Kelly Gravel, told CBS News. "We were looking at the barnacles -- it was quite unusual."
Less than a week later, Gravell found out something even more unusual.
The buoy her kids were playing with was actually a bomb.
"So the buoy my kids were jumping on all weekend turns out to be a WWII bomb. Oops!!" Kelly's husband, Gareth, tweeted.
Pembrey Country Park officials announced a temporary closure at West Beach in Burry Port Harbour "due to military mine found washed up" just five days after the Gravell children posed for pictures with it.
Park officials posted photos of the bomb on Facebook.
At first the parents didn't want to believe the news, but as they looked closer, they confirmed their worst nightmare: their children were playing with a bomb.
"It was a complete shock," Gravell said. "The story could have been a lot different had that gone off."
The next day, the Royal Navy detonated the estimated 30-year-old bomb from the U.S. in a controlled explosion.
Hundreds of people, along with the Gravell family, stood about 1,000 meters away to watch.
As everyone from the town clapped and cheered while the bomb went off, Kelly and Gareth looked at each other and their children in horror.
"We were thinking 'we're really glad that didn't happen at the beach,'" Gravell said.
Ellis looked up at his mom and asked, "are the little animals on there ok, mommy?"
Aside from news that stems from her husband, the coach of the local rugby team Burry Port RSC, Gravell says stories like this don't tend to spread to the rest of the world.
Although it's a fun tale to tell now, it's still a "what-if" memory that will stick with the family for the rest of their lives.
"In the future, we're going to approach [unkown objects on the beach] with care," Gravell said.