US admits killing more than a thousand civiliansWatch
Airwars (which generally leans towards being anti-Coalition in its outlook) estimates up to 11,637 civilians have been killed by the Coalition.
While each casualty is most certainly tragic, it is certain that ISIS and the Assad Regime have killed thousands (hundreds of thousands for the latter) more.
Estimates suggest that over 510,000 civilians have died since the war began; upto 85% of which are believed to have been killed by the Assad Regime and its allies.
This is from the Syrian Observatory for Human Rights (which is admittedly rather anti-Regime).