Glue - Glue is non-toxic, which means that you can technically eat it, though your body won't process it. It will still cause stomachaches if consumed too frequently. While it probably shouldn't be your next menu item, don't be too worried if your kid gets a little experimental.
Purslane - The weeds that typically grow in sidewalk cracks contain high counts of omega-3 fatty acid and are a tasty addition to many dishes. Just make sure they're in a clean area and not dosed with any pesticides.