The fast food industry spends a tremendous amount of money on advertising for a reason - it works.  Young children are especially likely to be influenced by the commercials they see.  Unfortunately though, fast food is a very poor food choice.  Almost all fast food is loaded with fat and is low on nutrients.  It should definitely not be consumed on a regular basis.  Have a family discussion about the impact of fast food on helath and explain that it something they can only have once in a while.  If your children are being influenced to the point that it is affecting their eating habits, you may want to consider limiting the amount of television they watch.