I wanted to make the room a total play haven for the kids and tried to make use of what little space we had to work with. We only have the kids once a month so their closet is also our camping gear storage area.
Basically the things the boys were interested in. They go crazy for anything with wheels, so I tried to insert as much as possible. I also tried to capture each child's interests and individuality while still sharing the room.
Eclectic. I try to go based on the interests and personality of the child rather than an overall theme since they're sharing a room.
The stores I found the items at were: Michaels for the wooden figures on the walls and the airplanes, Wal-Mart for the beds, posters, paints and oddly enough the dollar store for the alphabet posters.
The wooden figures and toys. I love wooden toys.
Just listen to your child's interests or for younger babies, go on what you think he/she might like.