First, your device passcode has likely become known to the local little people. This is Bad.
Second, for the granddaughter’s name substitution, you will want to check your settings:
… Settings > General > Keyboards > Text Replacement.
When you look there, I suspect you will find one of the local little people has added a text replacement there for that name.
On current software, you can use the Edit button to remove that text translation. (I’m not sure how far back that button goes, as your iPad Air 2 is both older, and not updated to its most current. An iPad Air 2nd gen should be running iPadOS 15, and not iPadOS 13 as shown in the footer here.)
Here is how to update to iPadOS 15, and which is the final version for iPad Air 2nd gen
Update your iPhone or iPad - Apple Support
Here is how to set or change a passcode:
Set a passcode on iPad - Apple Support
Allowing the little people to use an iPad can end Very Badly for the data. Several different folks I know well allowed that to happen, and lost precious photos and other important data.