Computers cannot generate truly random numbers. Why that is, and why it actually is an advantage for animators is demonstrated in this video tutorial by Frederik Steinmetz. Discover what a seed value is and when and how to use it.
Since computers can only generate pseudo-random numbers, you need to supply them with a seed, on the upside this means you can replicate the same result by using the same seed, thereby syncing entire simulations. In the animation nodes this gives you a lot of freedom when it comes to animating random numbers. If you do not have the animation nodes installed, you can find out how to install and use it here.
Here is the finished node tree to generate animated random numbers using the Blender animation nodes addon: