Animals can often recognize babies of another species...cats certainly can, and will often allow stuff from little kids that would get an adult scratched to pieces.
Siamese will try to defend the house against burglars sometimes (one of mine did not realise it was me coming home late one night, and was advancing on me like a banshee, looking supernaturally evil and making positively bloodcurdling noises....she was terribly embarrassed when she realised; stories of bailed up plumbers and suchlike abound).
I had a client whose very beloved cat appeared to bond with her baby in utero (a couple of colleagues are pregnant as we speak, and their cats are desperate to sit on their bellies with their ears to the baby, listening to the heartbeat, as far as we can tell)...this cat did that, and, when the baby was born, seeming to recognize that the mother could be abusive, set herself to protect the baby.
The mother told me that whenever she got unreasonably angry with her son, the cat got in between them and threatenrd the mother....had actually gone for her.
We used the cat's reactions as a good barometer to help the mother learn to back off and take some time out for herself when the cat stirred.
I think these cats, who would be used to caring for all kittens as a group, might well have recognized a "young", and incorporated it into their group.
The full article has more information about what they were doing.
That they were grooming the child really suggests it was seen as part of the group.