I don't actually know more than Wikipedia tells me, and it's been suggested that the yamanba may have been Kintarou's step-mom, but regardless of the blood relationship, she raised him.
And now that we have translation, it seems to be implying that this is actually the yamanba that raised Kintarou - but the fact that Mao-chan and Yamanba are having a tender moment means that Reiga can't ask if it's true right now.
Wait, does that mean we'll see Shuten and Ibaraki??
Wrong mountain. Mt. Ashigara is where Sakata Kintoki (childhood name: Kintarou) grew up. Mt. Ooe is where Ibaraki and Shuten's Oni gang dwelled.
The Truth Lies Within MemoriesMao!
I'll be givin' ye my wee one's old things!I'll just bribe her!Yamabaa...Hang on, bear...?!That Kintarou...?This bearskin is from the bear that my wee one often had sumo bouts with, too...An axe and bib!This is totally not the right kind of atmosphere to be asking about the whole "Kintarou" thing, is it...I'm right chuffed!Are ye comforting me?Hmm?Mao...?Cheer up!My, this brings me right back...It suits ye right down to the ground!The Mountain Witch... has kids...?Kintarou...