I read the raws and the WN, Akira uses "ore" in his speech and he's referred as the grandson of the family, so pretty sure he's an actual boy. ig he looks androgynous to emphasize his kindly nature.
Adding some info I read:
Sora (+Riku) 2-3 y.o
Koyuki (Sora's sister), Akira & Yui 5 y.o
Itsuki (Sora's brother), Takeshi - elementary school
Anyone dissing on Sora for pissing in his pants despite his adult's memories, remember chapter 1. Kid's just barely out of his diapers.