It started with a difficult choice. Surrender or save his pride. When Loki chose the latter, he marked the start of a strange accident, funny misadventures, and a realization that changed his miserable life.
Loki's dangerously weakened body changes itself into a six-year-old with no memory of what he has done. The Avengers cannot bring themselves to kill an innocent child, even if the child will grow up to blow up a city. Keeping Loki in the Avengers Tower will end with unexpected results, though. After all, this is the God of Mischief and the Trickster we're talking about.
Set after the Chitauri War, right before Loki says "I'll have that drink now." Ending will be sad.