Is there such a thing as "food safe" wood filler? Any tricks that would fill in cracks that would not require materials to be used that are toxic? Thanks.
Depending on the width and number of cracks, the diameter of knot holes, etc, you could make your own "filler" with matching sawdust and a bit of the glue you originally used.
Without seeing a picture, and with out knowing what glue you used, it won't be any more or less "toxic" than the rest of the cutting board if it doesn't look too bad. Hopefully, it won't be too noticeable.