I have the bed and it is wood, not plastic. The only think I would worry could be the canopy part. Although it is wood and very sturdy, if a preschooler sits on it, it could break since the canopy is made of three wooden kinda poles on top.
If your sure your son won't sit on the top of the bed, I think it's an excellent buy. This bed and Felicity's are my favorite beds. Plus I think this is a wide bed which means two dolls could fit on it.
Oh, I almost forgot, I did add a headboard cause the bed doesn't have a headboard and I like to put the pillows upright. I just used very hard cardboard and painted it white and it looks as if it were part of the bed.