Such a specific program probably doesn't exist, but the good thing is that it's a simple program and not hard at all to program. It would make a great beginner app and if you're up for the task here's how you might do it.

If you check the links in my sig, I have a tutorial on how to create an app that makes a slightly less pleasant sound than moo'ing. It's a great start and it contains all the code you need.

The tutorial shows how to use a button to play a sound. With Qt you can assign a background image to a button. Therefore add a cow image to button, replace soundfile with "moo.wav", and you got your first animal sorted. Repeat for as many animals as you'd like.

If nobody comes back with a ready made solution I hope you might give creating your own a try. Don't be afraid to ask any questions on the "Development" section of the forum if you get stuck along the way. The best part about creating it yourself is that you can tailor it exactly how your son would enjoy it