Here's my take, I'm a theme park minimalist. For me, and my extended family, carrying stuff we don't need almost always ends up being more hassle than value. Less is more.
IMO, the best option is just to share the device you're bringing for yourself +a sturdy carrying case.
I've taken many extended family trips to WDW, and a number of family disasters. Six + extra stuff isn't often a good combination.
What will you do if the child: forgets it on a ride, drops it on pavement, drops it into water, fails to protect it in the rain, or simply gets tired of carrying it? I've experienced all of the above and more. It wasn't fun when my niece lost a purse w/$50. Her mother admonished her the rest of the trip. A nephew left an electronic device in a ride pouch. Another niece hopped in the pool with a watch on her wrist. A cousin hopped in the pool with a phone in his swim suit pocket.
Twice family children had items knocked out of the hands by strangers in the crowd. Time A- a child had a toy knocked out of her hand when we boarded the monorail. The toy fell under the monorail. Oddly enough, that device actually showed up at the TTC's Lost and Found office a few days later! Time B, a set of ears was knocked off a child's head during the parade, despite the chin strap. It was never seen again, and we LOOKED!
In all the above cases, many tears were shed.
If you do get a device, give the child permission to lose/break it.
