We wound up only converting Claire's bed, because I can't really sit up and watch the children for longer than a few minutes. G took the girls up to see, and great fun was had climbing in-and-out-and-in-and-out. At bedtime, there was more crying than usual, mostly from Katherine -- I really think she wanted a bed too.
Both girls quieted down after about 5 minutes of crying, and we didn't hear any rumpusing. We heard a thump at about 10:30, and Claire cried a little bit, so we thought she might have fallen out. When G went up to check on her, though, she was still in her bed. Unfortunately, that woke both children up, and there was a few minutes of more crying before they calmed back down. At the final check of the night, both girls were asleep, and amazingly enough, Claire was still in her bed.
She was up at the nursery door this morning, of course, but didn't seem to have done anything other than play happily. Of course, we basically stripped the nursery of anything get-into-able, so there wasn't much she could have done. (Our nursery is upstairs, so it is literally just the room they sleep in -- all clothes, toys, diapering materials, etc. are downstairs.) Still, it seems to have gone well enough for a first nursery night.
We'll see how naptime goes in a couple hours.