One easy solution would be to have a simple central (e.g. Singleton) sound manager that controls playing those sounds. You'd notify that sound manager whenever a prefab is instantiated and then the sound manager could decide whether or not to play the spawning sound.

Obviously, you'd have to switch "Play on Awake" off (personally, I never use this because I prefer to have more control).

Then, in your sound manager, get a reference to the AudioSource of the object that was just instantiated, and use Play() to start playing the sound. You might keep references to the objects playing sounds and check if there's already too many playing already. One way of doing so is isPlaying (you might also check for null references in case those objects might already have been destroyed ... so be a little careful there).

That should give you a good start.