RE: Appen
I formally worked as a private contractor for one of the companies industry giants like Google farm this sort of thing out to. There were three, Appen Butler Hill, Lionbridge and Leapforce. Appen acquired Leapforce recently so now there's basically two. It was actually one of the best "at-home" job options out there, work when you want to, $13.50/hr.
The meat of the job was rating search results, which basically helped Google shape their algorithm to prioritize generally useful pages over useless ones. Some other tasks included slightly creepy shit like rating recognition of voice searches, especially for thicker accents. This was before it became common knowledge that every voice search you make when you "OK Google" is stored. You can search for it yourself on http://myactivity.google.com and listen to every voice search you've ever made. Interesting to note is that yes, saying "OK Google" is also part of the recording (i.e. it's always listening, which is why you get pushed ads for things you have verbal conversations for that your phone has overheard).
Basically my take on this email is Appen needs parental consent from Appen employees to record and use voice snippets from their children to overhaul voice recognition. Kids talk funny, have speech impediments, talk with food in their mouths, etc. so I imagine it's a little bit more difficult for the tech to transcribe their speech. Kids will have to sit down with their parents logged into their Appen work portal and will be prompted to say specific words and phrases which will be fed through recognition software and the parents will probably be tasked with correcting any transcription mistakes as part of their jobs.