The Hasbro pack was meant to be worn...technically. The original pack was very flimsy, and the straps were absolute trash. Rather than coming from the back of the pack like you'd think, they just put slits in the plastic wherever they wanted and looped them through.

So after removing the original straps and covering the holes with Bondo, I created a frame out of square aluminum tubing and mounted the plastic shell to that. This took care of the flexing, an gave me a rigid point to mount the straps.

The straps themselves came off some knock-off Mickey backpack I got on Amazon for $10. I cut them off, reinforced the edge with some stitching, and then popped grommets into them which I ran screws through. The idea was that this would let me securely mount them to the metal without running the risk of tearing through the material.

The final result was strong, but admittedly, not very comfortable. For long-term wear, I'd probably add some kind of padding over the aluminum frame. I also realized after the fact that the frame was mounted too low on the pack itself -- if I were to do it again, I'd make it slightly narrower so the top of the frame would be closer to the top of the pack. As it stands, the pack sits a bit too high on my daughters back.