In my family growing up eating out was a reward. At home you were given "stars" for good behavior and table manners, and if you achieved five stars in a row you got pick a restaurant to go to. As far as I can remember, none of us misbehaved in the actual restaurants, but since I had 3 siblings at the time, I was never the child to garner 5 straight stars. Probably because I counted on the others to get them and take us all out :P
As far as the situation described in the OP, I would talk to the manager. Talking directly to the parents could prove costly, and as someone operating a restaurant, it's probably in your best interest to calm the children down so you don't lose any business.