My toddler has black flecks or dots in stool sometimes. should i worry about blood or is it probably food he ate like raisins, etc?

Flecks are most: Likely food remnants. Blood would either be streaks or clots of red, or the stool would be more uniformly black & sticky. Probably ok.

Banana remnants: Black flecks in stool is often caused by remnants of bananas.

Stool flecks: Most likely it is something he ate and you are just seeing the "leftovers". If you are worried you can bring in a diaper an have your pediatrician test it.