Question: Before he was genetically altered and his real body was used, how did they get Chris Evans to look so scrawny?
Chosen answer: A couple of techniques were used. In most cases, Evans would film the scene normally, then the effects team would digitally shrink his character down to the smaller size. This would generally require some on-set adjustment to allow for eyelines - in some cases Evans would be physically lower than other actors, in others, they would look at his upper chest while he looked over their heads. In a few cases, actor Leander Deeny, who possessed the necessary scrawny physique, would film the scene, collaborating closely with Evans to ensure that the character's mannerisms remained the same. Deeny's features would then be digitally replaced with those of Chris Evans. Deeny appears briefly in the movie as the bartender in the pub Rogers visits to recruit his team.
Answer: When initially found by Odin, he does. Something then acts on him that causes him to mimic Odin's more human appearance, which he then keeps until his exposure to the frost giants during the events of the film, which tips him off to his true nature. Whether this was caused by some magic inherent in Loki even as a baby or whether Odin did something to disguise the child's true origin is unrevealed.
Tailkinker ★