Face id of 12mini is completely a failure

If you both are sitting in the same room and trying to open the device, then the chances of you facing the device for even a fraction of a second may open the device. Also, check if you have set up an alternative FaceID, remove it.

The way I see it, Face ID is going to be used everywhere in the future. Now many Airports use Face ID for boarding into Aircraft instead of scanning the boarding pass. During an immigration process also Face ID is being used.

It can't be as easy as you describe it. There is something that is amiss here.

If you are worried about security and do not trust technologies then please use a passcode to authenticate. Very simple.

Security safeguards

Security is important to all of us to protect the information on our devices. We have done some important things to safeguard your information, the same way we did with Touch ID. Face ID uses the TrueDepth camera and machine learning for a secure authentication solution. Face ID data - including mathematical representations of your face - is encrypted and protected with a key available only to the Secure Enclave.

The probability that a random person in the population could look at your iPhone or iPad Pro and unlock it using Face ID is approximately 1 in 1,000,000 with a single enrolled appearance. As additional protection, Face ID allows only five unsuccessful match attempts before a passcode is required. The statistical probability is different for twins and siblings that look like you and among children under the age of 13, because their distinct facial features may not have fully developed. If you're concerned about this, we recommend using a passcode to authenticate.