Enclosed my Autistic grandson's bed with curtains. Had concerns about using decorative curtain rods as I saw elsewhere as they could potentially be pulled down and cause injury. I put eye bolts into the ceiling. Used 1 1/2 inch PVC pipe with an elbow joint for the corner to run through the eye bolts. The materials for the frame were under $20 and an adult would have a difficult time pulling it down. I chose to use sheer curtain panels but any 84" curtains will work. He loves it!
@Overstock.com - Nathan Lined Blackout 84 inch Curtain Panel - Block out 99 percent of light in bedrooms, media rooms, and wherever else you need with these attractive grommet curtain panels. You will sleep better at night in the darkness these panels create. Choose from a variety of colors to match your decor. http://www.overstock.com/Home-Garden/Nathan-Lined-Blackout-84-inch-Curtain-Panel/6997320/product.html?CID=214117 $20.24
VCNY Nathan Lined Blackout 84-inch Curtain Panel by VCNY