The stolen child

"Henry Day, a boy stolen by changelings at the age of seven, and the look-alike hobgoblin sent to replace him, both grow up feeling out of place in their respective worlds--and their search for answers about their pasts puts them on a collision course decades later."@en
"A child is stolen by changelings who leave one of their own in his place, causing both boys to struggle to remember the lives they left behind."@en
"Seven-year-old Henry Day is kidnapped and renamed "Aniday" by changelings, ageless beings who inhabit the woods near his home. The changelings also leave behind one of their own, who flawlessly impersonates Henry except for one noteworthy detail--the new Henry is a prodigiously talented pianist. Both Aniday and Henry settle comfortably enough into their new existences, but both are haunted by vague memories of their former lives."@en
"Seven-year-old Henry Day is kidnapped and renamed "Aniday" by changelings, ageless beings who inhabit the woods near his home. The changelings also leave behind one of their own, who flawlessly impersonates Henry except for one noteworthy detail--the new Henry is a prodigiously talented pianist. Both Aniday and Henry settle comfortably enough into their new existences, but both are haunted by vague memories of their former lives.--"@en
"Seven-year-old Henry Day is kidnapped by the "Changelings" who live in the forest near his home, while a flawless substitute who happens to be a brilliant pianist is put in his place."@en