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Do Japanese children really color the sun red?
Literal
Really Japan [possessive-の] children [topic-は] sun [object-を] red-ly paint [explanatory-のですか]?
This touches on a well-known cultural difference: Japanese children typically draw the sun as red (from the Japanese flag and cultural association), while Western children draw it yellow. 赤くぬる ('paint red') uses the i-adjective stem + く as an adverb.