There are a whole bunch of food and hunger metaphors in "the mother." Think our gal Gwendolyn was just really hungry when she wrote the poem? Well, think again. Her food and hunger talk is a way for her to convey the strength, depth, and plain ol' bodily-ness of her feelings. Her feelings about her non-existent children run deep, and hunger is a great metaphor for making those feelings legible.
Line 6: This line introduces the word "sweet" as candy. (It's kind of an old-fashioned way to refer to candy, but we dig it.) But hold onto your horses, the speaker will use the word "sweet" differently in the poem as we read on.
Lines 9-10: The mother imagines having "a snack" of her children, and "gobbling" them up with her eyes. Is she expressing a Hannibal Lecter-ish desire to eat her kids? Probably not. It's just that she imagines loving them so much that the feeling is embodied. She has almost a physical craving for these kids (who, remember, don't actually exist in real life).
Line 14: The mother now refers to the non-existent children themselves as "sweets," as if they are delicious pieces of candy. Still, she won't be popping them into her mouth or anything like that. Calling her (non-existent) kids "sweets" is pretty much the same as your mom or dad calling you "sweetie."