This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/eek5W4YsSqC
Obvious tweaking for your specific head-board capping will be needed. It was designed slightly loose on the head-board so a thin rubberized tape (electrical tape) could be added to the inside of the bracket to add friction and protect the finish of the bed.

Bracket for attaching a small bucket or shelf to the headboard of a child's bed. In my case my daughters bunk-bed. It is designed to attach to a bucket with small hardware or wire-ties. There is a recess on the outer bracket (the thicker one) so the head of the strap can be recessed. You could also use double sided tape to attach a small shelf or bucket to the top plate of the bracket. Its a tight pressed fit so glue isn't necessary but still recommended or simply heat fuse the parts together. It is strongest and most stable when attaching to the top or inside bracket (the flat rounded plate). Print in a set of 2 or more depending on the width of the shelf or bucket you wish to support. Printed with 3 shells and .3 layer. No support needed.