It doesn't seem from the story like the babies are gladly sacrificing for the tribe...

"But..." said the Master. "But, my Lady, if they want to be eaten -"

"They don't," said the Xenopsychologist. "Of course they don't. They run from their parents when the terrible winnowing comes. The Babyeater children aren't emotionally mature - I mean they don't have their adult emotional state yet. Evolution would take care of anyone who wanted to get eaten. And they're still learning, still making mistakes, so they don't yet have the instinct to exterminate violators of the group code. It's a simpler time for them. They play, they explore, they try out new ideas. They're..." and the Xenopsychologist stopped. "Damn," she said, and turned her head away from the table, covering her face with her hands. "Excuse me." Her voice was unsteady. "They're a lot like human children, really."