Impossible to give your eInk Kindle or Kobo eReader to a Kid, as is or loan it.
if you remove the account you can't even add free eBooks and the EXISTING ebooks, bought or free, even if loaded via USB are deleted.
You can't use newer Kindle eInk or Kobo eInk eReaders AT ALL, not even add free books via USB without creating an account.
Only solution seems to be to create an eMail account for kid / friend (Kobo) with no credit card. Amazon seems to need a credit card and no way to disable small kindle book purchases via WiFi or 3G (so only give kid WiFi model and keep wiFi keysecret, but they might use library / friends house?).
So the way accounts / purchases work on eInk Kobo or Kindle you buy, even for your own writing or public domain books is unacceptable today. Esp. Amazon. Kobo, at least you can create an account with no payment option.
Don't lend your Kindle / Kobo to ANYONE!
Back up all the books via Calibre / USB, as ANYONE my fiddle with settings, remove your account (no security PIN on Kobo) and thus delete everything!
The password protected Kids Mode on Kindle hides all free books, everything not purchased from Amazon. It's USELESS.