Accidentally deleted photos and videos

Any deleted photo/video will go into the Recently Deleted folder in the Photos app and will remain there for 30 days in case you change your mind.

If it has been longer than 30 days or you deleted the photo/video from the Recently Deleted folder, then they are gone for good from the Photos app. When you delete from the Recently Deleted folder, you see a message that says if you continue, they will be permanently deleted and that is exactly what it will do.

That's awful! You didn't say if you are using iCloud Photos. If you don't use iCloud Photos, but you have Settings>Apple ID>iCloud Backup turned on, then you may be able to recover data. You should look here:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support 

“Restore” is what you do when you buy a new phone, so this safety, if you have it set, requires you to erase everything on your phone and replace it with the backup.

If you have iCloud Photos, then everything you do on the phone is quickly copied to iCloud, so iCloud Photos doesn't serve as a backup against mistakes.

Unfortunately, if you don't keep your own backups to an external drive, then there really isn't any place else to look.