Well, to me that is the parents/adults fault. The end of the harness should never be left loose. It should always be in an adult's hand. If they had been holding it then it wouldn't have ended up caught in something. If you want to let the child wander you can either remove the harness/backpack completely or remove the strap (they can all be detached). You don't just let them run dragging the strap. I'm still very sorry to hear it happened - and I'm sure the parents are hurting emotionally also (at least I know I would be if I had been in that situation). I realize you were just sharing a word of caution and I agree completely. It's like anything - you MUST use common sense. It's absurd all the warning notices they have to put on things because our society doesn't think first...
And just for a chuckle:
Manufacturers of consumer products have to be liberal with the warning labels these days, lest they get sued. But for these, it's hard to know whether the company is being outright stupid or if they're simply targeting the most brain dead dumb among us.
Product Warnings:
"Do not use if you cannot see clearly to read the information in the information booklet." -- In the information booklet.
"Caution: The contents of this bottle should not be fed to fish." -- On a bottle of shampoo for dogs.
"For external use only!" -- On a curling iron.
"Warning: This product can burn eyes." -- On a curling iron.
"Do not use in shower." -- On a hair dryer.
"Do not use while sleeping." -- On a hair dryer.
"Do not use while sleeping or unconscious." -- On a hand-held massaging device.
"Do not place this product into any electronic equipment." -- On the case of a chocolate CD in a gift basket.
"Recycled flush water unsafe for drinking." -- On a toilet at a public sports facility in Ann Arbor, Michigan.
"Shin pads cannot protect any part of the body they do not cover." -- On a pair of shin guards made for bicyclists.
"Do not drive with sunshield in place." -- On a cardboard sunshield that keeps the sun off the dashboard.
"Do not use near fire, flame, or sparks." -- On an "Aim-n-Flame" fireplace lighter.
"Do not eat toner." -- On a toner cartridge for a laser printer.
"Not intended for highway use." -- On a 13-inch wheel on a wheelbarrow.
"This product is not to be used in bathrooms." -- On a Holmes bathroom heater.
"May irritate eyes." -- On a can of self-defense pepper spray.
"Caution! Contents hot!" -- On a Domino's Pizza box.
"Caution: Hot beverages are hot!" -- On a coffee cup.
"Caution: Shoots rubber bands." -- On a product called "Rubber Band Shooter."
"Warning: May contain small parts." -- On a frisbee.
"Do not use orally." -- On a toilet bowl cleaning brush.
"Please keep out reach of children." -- On a butcher knife.
"Not suitable for children aged 36 months or less." -- On a birthday card for a 1 year old.
"Do not recharge, put in backwards, or use." -- On a battery.
"Do not use for drying pets." -- In the manual for a microwave oven.
"Warning: Do not climb inside this bag and zip it up. Doing so will cause injury and death." -- A label inside a protective bag (for fragile objects), which measures 15cm by 15cm by 12cm.
"Warning: has been found to cause cancer in laboratory mice." -- On a box of rat poison.
"Do not turn upside down." -- On the bottom of a supermarket dessert box.
"May be harmful if swallowed." -- On a shipment of hammers.
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In summary, read the paper that comes with the backpack. I'm positive it will say to not let the child wander with the strap hanging loose. If I remember right from my bear one, it also mentioned the tripping hazard (if the child darts in front of people they could trip on the strap between child and adult) etc.