Fireflies is an enjoyable app for both kids and adults alike. To get the maximum effect, I recommend you play with Fireflies in the dark. Reminiscent of childhoods past, you’ll soon be immersed in the sound of crickets chirping their nighttime serenades as you gently reach out to capture the fireflies, flickering in and out between the cattails. This is relaxing entertainment. Your kids will love it, too!
Fireflies and childhood development
While this may stimulate memories of "childhoods past" it may also be even more useful exactly as you're suggesting at the end, particularly for introducing "new" auditory and some visual stimulus for infants, while I never really saw any solid evidence that exposure to classical music in vitro was beneficial, infants and young children are like mini-radar picking up on everything in their environment, so exposure to a variety of stimulus (as long as it's not overwhelming) is beneficial. My family being bi-lingual, we took care early on with my son to expose him to Hungarian language and sounds early on.
Now I'm also thinking that this may be useful for me as part of a relaxation routine, similar to my white noise machine.