Amazon & the FTC have reached an agreement over unauthorized in app purchases made between November 2011 and May 2016. Amazon did not require a password for in app purchases during this period, this allowed kids to make purchases without their parents permission. A password requirement was added in 2012, but this was only for purchases over $20. Amazon is sending out e-mails to those who might be eligible, you can also check this link to see if you have any eligible purchases.
If a child under the age of 18 made purchases without your authorization you have until May 28th, 2018 to apply for a refund. The FTC expects up to $70 million to be eligible for a refund. You can also call 866-216-1072 to check the status of your refund.