You know the ones that sit right behind you and shriek right over the person talking so you only catch half of every sentence. I know it's not the child's fault (duh!) and sometimes you just have to bring them along BUT why don't the parents move away towards the door or back of the hall so that the other parents can hear?
Also if theres an assembly in progress why do some parents think it's ok to let their toddler wander off in front of the stage to ruin it for whoever might be doing their bit of the performance?