How do I lock iMessages on my iPad
iPad Pro Wi-Fi, iOS 11.3.1
No, you cannot lock or password protect any built-in apps. iOS devices are considered to be personal; you can lock the device, but not individual functions.
I think you mean, "restrictions" ..
How to use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support
No, when I go to settings and under messages, when I turn on imessage, is there a way a passcode can be entered to access? I’m not seeing messaging under ‘restrictions’
How do I lock iMessages in my iPad
