So my youngest child has managed to lost one of my rented books, how can I "replace" the book and how does it work? Thank you.

Hi! You can either pay the book in any of the HelMet-libraries or replace the book with a same book.

From our user regulations:

"Compensating for items and paying the fees
You will have to compensate for lost or damaged material by paying a price which is charged according to the item’s value registered in the library’s database. If you wish to substitute a similar item for the material lost or damaged, you will have to settle each case separately with the library."

http://www.helmet.fi/Preview/en-US/Info/Using_the_library/Fees(37613)