It has happened, at least to some extent, with ground squirrels, which are more likely to deliver warning calls in the presence of close kin. It has happened, to some extent, with chimpanzees and other non-human primates, which often have uniquely supportive relationships with siblings. And it has happened, to a great extent, with us. Maybe the world would be a better place if it hadn't. But, for better or worse, the literal kind of brotherly love is the kind we have.
Many social insects recognize their kin with the help of chemical signals called pheromones.
Surely seeing our mother feed and care for a child day after day is one conspicuous cue. We may also, by observing our mother's social affiliations, develop a sense for, say, who her sister is, and hence who her sister's offspring are. It's hard to say what other kin-recognition mechanisms, if any, are at work, since experiments that would settle the question involve unethical things like removing children from families. What's clear is that mechanisms exist. Anyone who has endured a sibling's death is familiar with grief.