Indians killing infants or small children when taking captives was very very common. They slowed down escaping and traveling back to camp and preoccupied the slaves from being hard workers and were merely useless eaters if taken alive . Brain dashing was the normal method.
Older captured children were sometimes kept if they could keep up with the march, and had potential as adoptees or workers.
Hannah adopted the culture and values of her captors.
Actually indians took lots of little children, toddlers, and infants, many they killed at the home like you pointed out but they took many to keep or to ransom, it was common for children that little to cry too much, or become a problem, or perhaps to annoy the mother, the indians or a single member of the group would decide to murder them, often cruelly, and sometimes even with torture, and they would scalp the little ones also and bother the mother and/or siblings with the wet and bloody scalps if they were alive.