Why is it hard for a program to generate random numbers?
random
Solution
How about, "Because computers just follow instructions, and random numbers are the opposite of following instructions. If you make a random number by following instructions, then it's not very random! Imagine trying to give someone instructions on how to choose a random number."
Problem
My kids asked me this question and I couldn't really give a concise, understandable explanation. So I'm hoping someone on SO can.