Can a parent sign away a child's rights by signing a waiver of liability? Not in Kentucky (and many other states)

Those of you who have children out there are familiar with this, which as a parent myself, I have seen and done lots of times!  Your child wants to participate in a sport or other physical activity, and you (the parent) are asked to sign a "waiver" before the child can be allowed to do so.  Will those waivers really work to prevent a lawsuit?  Are they a valid form of contract that can be argued support a defense of express assumption of the risk.  Not in many states.  (I have not done a state by state survey, but I suspect this would be the case in a majority of states.) 

The Torts Prof blog is reporting that the Kentucky Supreme Court has unanimously ruled that for-profit companies can be liable for injuries to minor children even if their parents signed a pre-injury waiver.  The ruling came in a case in which an 11-year-old girl broke her ankle jumping on a trampoline at the House of Boom in Louisville, KY in 2015.  The mother had checked a box saying that she, on behalf of her daughter, would "forever discharge and agree not to sue" the trampoline park.  The court noted that for the most part, under Kentucky law, "a parent has no authority to enter into contracts on a child's behalf."  The court also stated that in 11 of 12 jurisdictions in the U.S., waivers between parents and for-profit entities have been found unenforceable.  WDRB.com has a little more on the story.