As per Anil K Jain, Lifefellow IEEE
"We show, for the first time, that fingerprints acquired from a child as young as 6 hours old exhibit distinguishing features necessary for recognition, and that state-of-the-art fingerprint technology achieves high recognition accuracy (98.9% true accept rate at 0.1% false accept rate) for children older than 6 months. Further, using mixed-effects statistical models, we show that the recognition accuracy is not significantly affected over the one year time lapse in our data."
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He says that even the prints collected from a 6- hour old child are unique and sufficient to identify him . And even after a period of 1 year, the baby can be identified by the same prints.
He also says that
"Biological evidence, on the other hand, suggests that fingerprints are fully formed by the sixth month of fetal life and are physiologically present on human fingers at birth "
What he is saying is that fingerprints are fully formed by the time the child is born, and so prints can be taken at birth itself. There is no need to wait for 6 months after the birth.