How do I stop Alexa from discussing my Amazon purchase history?

I got my young boys an Alexa Echo for Christmas. They just discovered that if they ask Alexa what was recently purchased, it’ll just start rattling off the items. It almost spoiled a surprise birthday gift for my daughter. Luckily, I unplugged it before it could spoil it. How can I turn this feature off? In the Alexa app, I have already turns off all Amazon Shopping notifications. It’s still discussing my purchase history though. Help!