Corrected entry: During one of Sam and Sophie's private talks, Sam says he has two grown sons. He went home and got married after Sophie had been conceived, therefore his oldest son could not be older than 19.
Corrected entry: Right after Sam, Bill, and Harry arrive and they are all in the goat house with Sophie, they hear Donna humming something, which prompts Sophie to run out abruptly. Listen more closely to what Donna's humming. It's "Fernando", another hit ABBA song.
Correction: The entire soundtrack to the film consists of ABBA songs. Pointing out one of them, even one less obvious that those that are actually sung, is not a valid use of trivia.
Correction: The age of 18 is considered to be the age a child becomes an adult and thus considered a grown child. It is indeed physically possible he has children the ages of 18 and 19 or even twins.
OneHappyHusky