Given that a quality air bed is purchased, almost all of the things which were once issues should no longer be areas of concern. Any air mattress is susceptible to the same types of problems as any other air mattress.
Inflatable air beds may not be the most comfortable kind, because you certainly can adjust the mattress to meet your needs like you can with another adjustable bed. Mattress beds that are too firm will not allow for the natural and essential curvature of the spine. When your child is ready, pile the beds into the standard bunk bed arrangement.
Avoid falling for models that give other features such as digital controls, slow and quiet pumps and layers of foam that are not necessary and add a huge chunk to the price tag. Twin beds are commonly used for the bedrooms of the children and for multi-user guest rooms. It also seems that the dual wave beam construction of the bed made it more stable and comfortable, especially when used by two people.
Other brands can be just as plush and some can be a lot less expensive. Today's stacked bunk beds are suitable for children ages five and above, but you will be the best judge of when the appropriate time is for your child.