House key: 10,700 ppm lead.
The current amount of lead that is considered toxic in an item intended for children is anything over 90 ppm lead. Items intended for adults (including dishware and keys) are generally unregulated for total lead content as they are not designed or sold as intended for children. Keys specifically are made with lead to increase the lubricity and support their function, however it is possible to make lead-free keys and lead-free are available for purchase at many hardware stores (they are just a bit more brittle than most keys and need to be used a little more gently than you might otherwise use as key – as they could break off in the lock. #ExperienceSpeaking.]
Advice / takeaway: Don’t let children (especially babies – or any other child who puts things in their mouth) play with real house keys. But them a child-safe toy set instead.