Isaac Burnett, 10, and his eight-year-old brother Lukas, from Stirling, are both living with the degenerative muscle disease muscular dystrophy.
Isaac was diagnosed with the condition in September 2006 when he was just three years old. Lukas was checked for the disease shortly after and was diagnosed three months later.
The brothers are on steroids, which slow down the immune system and help retain muscle. They attend several hospital appointments a month and both use wheelchairs.
The life expectancy for the brothers is unknown.
Their day trip to Legoland in Windsor was set up by the Make-A-Wish Foundation UK as they both love playing with Lego, especially as an escape from treatment.
Tina Burnett, the boys' mother, said: "The trip to Legoland really cheered the boys up."