What would happen on a farm if the farmer killed all the owls on his property because he tought that they were pests and his children were afraid of them?

The number of rodents and other animals that fall prey to owls would increase which may create a problem in itself by the little animals eating more of the plants that grow on the ground; it messes up the food chain. But for the comfort of the family (if harmless mice running around wouldn't bother the children), at least eliminating part of the owl population might be a good idea.