seems Facebook changed the result of posts, few weeks ago it was possible to read the comment count from the post directly
https://graph.facebook.com/125909647492772_502
Or to make less changes to you excisting code, use:
$.each(json.data,function(i,fb){ ... var commentsCount = 0 if(fb.comments!=undefined){ commentsCount=fb.comments.data.length } ... }
commentsCount holds number of comments for active child