Hello robinfrommontgomery,
It sounds like you are missing an app after logging into the Apple ID.
Here are some resources that can help:
If it's the case that you restored a backup from the iPad to the iPhone, it could be expected as seen under "Can I use my device's backup for another kind of device, like an iPhone backup for an iPad?" in About backups for iPhone, iPad, and iPod touch
Either way, you can try to redownload the app from the App Store: Redownload apps and games from Apple
If you are getting the message that it is blocked when downloading the app on the iPad check the settings for "Prevent iTunes & App Store purchases" in Use parental controls on your child's iPhone, iPad, and iPod touch. If it happens when trying to use the app check out "Prevent web content" in the previous article as well as Screen Time settings such as App Limits or Downtime in Use Screen Time on your iPhone, iPad, or iPod touch.
If you have the app and the block is specific to this app, you may want to check out Messenger Kids | Messenger Help Center | Facebook.
Hope this information helps.
Have a good day.