Originally Posted by
kash
Something rather strange from the hotel's reply is: "For safety reasons, children of elementary school age and above are required to have their own bed.". I don't know what kind of "safety" the hotel is talking about that children need to have their own bed. How would that be safer?

Child becomes “adult” at 12 in most Japanese hotels (those that don’t exclude them entirely).
Worth noting that the age of consent is still 13 in Japan.
If the second child is still under 12, there are quite a few hotels with a “child stays free if using existing bedding” exemption. In the past, I’ve made award redemption bookings that don’t accept kids in the search criteria for two adults and then contacted the hotel after the fact to advise them that a child using our bedding was staying with us. In your case, you’d need to find a hotel that allowed a child to share bedding in a room booked for three adults.
We found the process quite tricky at Western Hotels and only had the one child (she’s 13 now). It is rather more straightforward at Japanese style lodgings.
Or see if any of the options in that other thread suit your family.