Face recognition is one of the first visual skills Baby learns – a 2012 study out of the Stanford Vision and NeuroDevelopment Lab says that babies can process faces almost as well as adults do by the time they’re around 4 months old. Other studies suggest that babies can recognize their parents or primary caregivers’ faces within days or weeks, and their mothers’ faces sometimes within hours of birth, depending on how awake and attentive they are.
Once Baby starts building the skills to differentiate between faces, which they start working on pretty much as soon as they are born, the biggest factor in when they start to recognize the people in their life has to do with how often they see them, and for how long. The first people they recognize are generally their parents or primary caregivers – the people who feed them, and whose faces they get to see up close and personal for significant amounts of time even when they're young enough that they can only see approximately 8 to 12 inches from their face. This means that if Baby only sees their grandparents once every couple of weeks for a few hours, it might be a few weeks until they start to recognize them, while family or friends who they see once a week will make it into Baby’s mental roster of friendly faces a little faster. And people who drop into their life every day, even if they’re, say, the crossing guard near their daycare, rather than an adoring relative, will be someone they recognize pretty quickly.