In this story the alien baby keeps taking bites of different things and, finding them inedible, spits them out. A human boy finds them and understands that the baby needs food (I don't remember if the mother ate or not). The human boy tries to help them by bringing them all sorts of food.
I know the ending and I've tried to block it:
The story ends when the baby actually takes a bite of the boy and finds that he is edible. The mother then loads up the baby and they leave. I found it touching that the mother would risk starvation for her and her baby rather than hurt this boy who had tried to help them.