I already know the answer, but I gotta ask anyways, why don’t authors just make the character like teenage or a young adult instead of a child if they’re not going to write the child like a child? It’s just a peeve of mine when I see 6 year olds act with the same (or higher) maturity/social awareness than people a decade older.
Comedy is a set of overlapping frames of reference. Frame A is an innocent children. Frame B is a worldly woman. Overlapping the two creates comedy.
Of course, execution matters. Sloppy execution (e.g. draw child, make her into lingerie, …, profit!) makes for lame comedy. Good execution would be where the two frames are set up to both be very strong, contrasting, yet coherent; where we can never tell which way the character is going to go in any given moment but it always makes a certain degree of sense. Then it is surprising and fresh.
Makeine has a great imouto character. She’s both strongly child-like and also acts like a meddling superstitious old woman. It is played in a manner that feels both internally consistent to the character yet unpredictable to the reader.