Hello bdavblank,
Welcome to Apple Support Communities.
Congratulations on the newest additions to your family. We understand that the birthdays of two of your grandchildren are not showing correctly in your calendar. We are happy to help.
So that we can isolate the cause further, we’d like to have you complete some isolating troubleshooting steps—safe mode and testing in a new user account.
Safe mode: Use safe mode on your Mac - Apple Support
"Test in safe mode
Follow these steps after starting up in safe mode. Some features might not work in safe mode, affecting video capture, graphics performance, file sharing, Wi-Fi, accessibility, audio devices, and devices connected via USB, Thunderbolt, or FireWire.
If the issue continues in safe mode
If the issue continues in safe mode, the easiest and most likely solution is to reinstall macOS. Reinstalling macOS doesn't remove your personal files, so you can do it whenever you need to.
If the issue doesn't continue in safe mode
Leave safe mode by restarting your Mac normally, then try to reproduce the issue. If the issue doesn't return, it might have been resolved by the other things that safe mode did at startup, such as checking your disk and clearing caches.
If the issue returns, it is caused by a login item or other software that safe mode prevents from loading at startup. In that case, remove login items to find out whether a login item is at fault.
If a login item is not at fault, your user account might contain other software that is incompatible, including certain software that loads at startup. To confirm, you can add a user account in Users & Groups settings, then log in to that account and test again. The new account won't have the same settings as your old account, but you can create those settings again.
If nothing else works, reinstall macOS. Reinstalling macOS doesn't remove your personal files, so you can do it whenever you need to.
If you still can't resolve the issue and need help, please contact Apple Support."
Add a new user account: Change Users & Groups settings on Mac - Apple Support
"Create a new user or group.
Click the New Account pop-up menu (you may be asked to enter your password), then choose a type of account.
- Administrator: An administrator can add and manage other users, install apps, and change settings. The new user you create when you first set up your Mac is an administrator. Your Mac can have multiple administrators. You can create new ones, and convert standard users to administrators. Don’t set up automatic login for an administrator. If you do, someone could simply restart your Mac and gain access with administrator privileges. To keep your Mac secure, don’t share administrator names and passwords.
- Standard: Standard users are set up by an administrator. Standard users can install apps and change their own settings, but can’t add other users or change other users’ settings.
- Sharing Only: Sharing-only users can access shared files remotely, but can’t log in to the computer or change settings. To give the user permission to access your shared files or screen, you may need to change options in File Sharing, Screen Sharing, or Remote Management settings. See Set up file sharing and Share the screen of another Mac.
- Group: Groups allow multiple users to have the same access privileges. You control a group’s access to your shared folders by setting access permissions in the File Sharing options in Sharing settings.
See Add a user or group."
These steps may help. Let us know if you have further questions.
Take care.
