There are many rumors that Chibi-Usa is not the daughter of Mamoru and Usagi because of her red eyes and pink hair. Many people like to say that Chibi-Usa is the daughter of Setsuna and Mamoru, which would explain the red eyes. But it would not be genetically possible for Chibi-Usa to be the daughter of Setsuna and Mamoru

Both Setsuna and Mamoru are type A blood. Chibi-Usa has type O blood. A is dominant over O so Setsuna and Mamoru would not be able to produce a type O child. Chibi-Usa has to be the daughter of Usagi and Mamoru.