Actually, the comments on the pixiv page hint at one parent being Yuuka. Makes more sense that way, considering the lack of froggy things, the red eyes, and the messy-looking hair.
Kanako wasn't ever in doubt. The shimenawa bracelets and red leaf headband made that certain. The point in question was whether Sanae or Yuuka was the other parent (note the tagging history).
However, I'll retract my earlier position; it seems that the artist just wanted to draw the Sanae+Kanako lovechild with Yuuka's messy hairstyle.
I think it's odd to leave out the frog motifs entirely, but whatever.
