Crumbs revision 1

[Leanne]

My childhood lay behind me -- this is an oddly ambiguous opener.  If childhood once lay behind, wouldn't it still?  In which case, you would probably choose to use "lies" instead -- so this leads me to believe that either this is an accidental slip of grammar or time is not following that standard arrow here and what was past has become something other
in this trail of torn bread -- "torn bread" is a strong choice over "breadcrumbs", not only because it avoids the cliche trap but also because of the violent connotations of "torn"
I could no longer retrace. -- again we have the grammatical oddity of "could" -- does this imply that he would if it were possible?
 
We always ate enough
to remain hungry, our stomachs -- good break on "enough", and an excellent near-paradox
waning like the sliver of moon
that sparkled through the branches -- "sparkled" coupled with "darkling" seems too much of a choice of sonics over substance -- I have difficulty with the use of a simile comparing stomachs to something sparkling
of this darkling forest.
 
Even when I saw the food
on her table, I kept gnawing
on the shingle like
a little mouse, little mouse. -- this stanza fascinates me.  I see the mouse as a scavenger, occupying space only at the very slender mercy of its rightful inhabitant, and yet the table full of food implies that it is there for the taking, but rejected.  To me, this represents the offering of knowledge and the choice of ignorance. 
 
I still carry the finger bone
I once pressed into her hand
each night, while licking the plates clean. -- I can't help but think that the finger bone is his own, somehow removed, now carried as a kind of penance.  This would indicate a tentative but still close relationship between child and mother, or prisoner/captor, student/mentor.  
 
The hunger had crossed the threshold with me, -- a physical crossing, but not psychological, and it's in the mind that reality dwells
and remained even -- "even" gives a nice ambiguity as a break, as both "equal" and "still"
as her fat melted in the oven. -- the fat she cooked with, or the fat on her body -- again, lovely open meaning
 
We came back older than our parents -- this brings me back to the idea of knowledge/ experience
with gems that shone like in the fairy tale
of the girl who had them fall from her mouth
like so many ripe cherries. -- too many "likes" here -- you are running over your simile allowance!
 
I chewed my words until they broke -- this imparts a strong sense of regret, words spoken in the fullness of youthful brilliance without regard for feelings, and impossible to recall
my teeth, and laid heavy in my stomach
like forest stones.
I no longer needed a path back -- this is a nice bookending, but the "for" on the next line weakens it somewhat.  I would suggest 

I no longer needed a path back:
I never left that cottage

for I never left that cottage.