If nobody mentioned it yet, you might check with the CPSC to see what they require for product certification, especially if it can be used on children's bikes. Liability and consumer protection issues often over-ride design and manufacturing issues. Good luck.

Years ago I came up with a series of bicycle trailers but never got to the manufacturing point. Manufacturing cost was one factor, ability to defend the product from competing companies was another big factor and my pockets weren't deep enough to pursue it.