According to a security guide published Wednesday, Apple recommends that children under the age of 13 do not use Face ID on the iPhone X due to the probability of a false match being significantly higher for young children. The company said this was because "their distinct facial features may not have fully developed." They also recommend that twins and siblings do not use the new feature. The Guardian reports: In all those situations, the company recommends concerned users disable Face ID and use a passcode instead. With Face ID, Apple has implemented a secondary system that exclusively looks out for attempts to fool the technology. Both the authentication and spoofing defense are based on machine learning, but while the former is trained to identify individuals from their faces, the latter is used to look for telltale signs of cheating. "An additional neural network that's trained to spot and resist spoofing defends against attempts to unlock your phone with photos or masks," the company says. If a completely perfect mask is made, which fools the identification neural network, the defensive system will still notice -- just like a human.