"We actually thought we would take a week to make the trip, but then we didn't have time. We thought we might have to take the train for part of it," the boy's mother, Linda Blomdahl Petersson, told The Local.
"But then on the first day we biked 103 kilometres, and we thought, 'This may actually work'. When we booked the trip it felt like a half crazy idea."
The family took their bikes to the Swedish town of Trelleborg, cycled onto a ferry to Rostock – and began the trek.
Their most recent biking adventure was on Öland, but the journey was much shorter.
"On Öland we only biked three kilometres a day," seven-year-old Edvin Blomdahl told The Local. "But we biked 103 kilometres on the first day, and 99 on the second day."
After that Blomdahl lost track. But when The Local asked if it was difficult or wearisome, his response was clear: "It was just fun to cycle."