Why did the men consider leaving Salva behind?

From the text:

The woman put her hand on Salva's shoulder. "This one is alone. Will you take him with you?"

Salva saw doubt on the people's faces. Several men at the front of the group began speaking to each other.

"He is a child. He will slow us down"

"Another mouth to feed? It is already hard enough to find food"

"He is too young to do any real work—he'll be of no help to us."