If you utilize Apple’s Face ID technology, which unlocks iPhones by identifying the user by glancing at the device, your child, parent, or another close family member may be able to unlock your cellphone without your permission.
Face ID, which has difficulties distinguishing between close family members, appears to be fooled at times by the resemblance of their appearances.
While it was previously established that FaceID had difficulty distinguishing between twins, such a failure affects only a small fraction of the population; persons who are not twins, i.e., the majority of people, were thought to be safe.
That view altered, however, once researchers discovered that the problem is considerably more serious; the fact that FaceID sometimes fails
Why can my daughter’s face open my iPhone?
If your daughter knows your iPhone’s passcode, the gadget may have learned to recognize her as well. Face ID reacts to changes in your look automatically. It is continually learning to recognize you.
If your appearance has changed significantly, by entering the proper passcode, you are instructing your Face ID to update your face data. So, if your daughter unlocks the iPhone by entering the proper PIN, her face is most likely added to face data as well.