story identification - Fantasy novel with assassins and orphans

I read this book back in the 90s, I believe. It was a fantasy novel took place mostly within a city. All I can remember is that there was an assassin that was going to kill a king and there were orphans or street urchins involved in the assassination. I believe it took place during wintertime. I think it had knights and mages and creatures the army fought in a forest. The assassins weren't the main characters. I think the assassins were the children or there were children who witnessed the assassin preparing for the hit, killing a couple of guards and then he murdered them or it could have been the assassin was preparing for the hit and was killed by the children. I just remember them as being a plot point that stuck out.