ah come on. It's halloween. Brothers dress up as their sisters, sisters dress up as their brothers, kids dress up as their neighbours.

You are an acceptable costume. Face it. But context matters. The reading kid is not singled out, nobody is making this negative. It could also be perceived as a celebration 'hey I want to be like my adopted asian sister, she is cool'.

Live and let live, and give context if the kid is asking questions. But don't censor because you feel like a special snowflake