We booked for one adult and one child through the Hotels.com system. When entering a child, you're required to enter the age. We did that - 14yrs old. The price is more than just one adult. That is normal. BUT when we got to the hotel they told us we had to pay an additional 3000yen because my daughter is 14yrs old. We showed them our booking confirmation, but they didn't care. They just wanted their 3000yen. I don't know if it's a problem of Hotels.com/Expedia or the hotel, but we shouldn't have to pay even more when we have a confirmed paid booking for 1 adult and 1 14yrs old child already.
The room itself was nothing special. Small - which was expected. Clean enough. No special reason to stay here. Would recommend against staying here if you have children.