This is going to be a family_friendly story. The story narrative jumps around and rambles a bit more then I had planned but I think I'm going to go with it.
Yukkuri are a pet unlike any other. They have a capacity for speech and near human intelligence. They have cultural mores and behavior patterns they inherit from one of their parents. They have a sociability that lets them be at ease with human ownership. Such an unusual combination of traits can't be matched by any other creature.
At the moment I am raising two koyukkuri, a Reimu and a Marisa. I adopted each of them from different friends whose pet yukkuri became pregnant over the winter. I really had the pick of the bunch, Reimu's artless coyness and Marisa's confident and adventurous attitude are absolutely adorable.
Normally, I raise two koyukkuri of the same type from the same stalk. Yukkuri have a natural disinclination to mate with another yukkuri of the same type. There also seems to be a reduced interest between yukkuri who are related. I also give them koyukkuri dolls which seem to satisfy their parental instincts.
However, one time I returned home to a pair of my yukkuri and found that one of my Reimu had a birthing stalk with four little koyukkuri. I was momentarily at a loss but I found what I think is an elegant solution to the problem. I separated the yukkuri living area into two sections with a fence between them. The slats have gaps large enough to let koyukkuri through but by the time they are old enough to 'refresh' they no longer fit. The slats are thick enough that they can't reach between them, even with an Alice's 'braggable peni-peni'.
The Reimu were upset about the separation at first but grew to accept it after I gave them supervised time together. By the time their little ones were born they forgot all about it. The kos in particular seemed to enjoy the fence, puff-puffing at their parent on the other side. The other parent would creep up slowly-slowly behind them and puff-puff at them teasingly and chase them to the other side of the fence where the game would start all over.
Eventually the kos grew up and would no longer fit between the fence. I spent an entire afternoon drawing out different pen arrangements that would maximize large living areas but allow each yukkuri to see each other using a complicated arrangement of runs between areas and common areas. I was considering multi-level structures and closed circuit television systems when I realized I was thinking too hard about it.
In the end I simply put a pair of kos and one of their parents in each area. It seems that the incident with their parents was anomaly because the yukkuri lived the rest of their lives without another birthing incident.