I'm thinking that there's more to it than what's here.
When an adult can't restrain a 6 year old, there's an issue, either with the adult, or with the 6 year old. I'm wondering if she was handcuffed to avoid hurting herself.
And the bit about her complaining that "They were tight", well, that's what handcuffs do.
Obviously the adults could have restrained her without handcuffs. That would have involved holding her physically for an extended period. Parents would then claim sexual assault.
I'm with you. Even the Chief of Police ‘defended the action’, according to the reports.
Too bizarre otherwise methinks.