Some people such as the author of "Raise a smarter child by kindergarten"  David Perlmutter suggests that TV and other artifucial lights can cause early puperty.  "TV viewing as well as prolonged exposure to artificial light suppresses the production of a hormone called melatonin that helps regulate sexual development...Artificially suppressing melatonin, however, could cause a child to go into puberty prematurely." (106)
But I don't see how using flash cards for a few minutes a day would be a big problem.  You also have the option of printing them out... so you can limit the time even more.

The gifs such as walk etc.  Slower moving objects might be easier for babys to focus in on.

Things that children will see outside. 

Maybe some easy to read stories: Jane went swimming.  She likes swimming..

I also think that there could be files to download by level/ instead of category inorder to help parents who aren't sure where to start or how much a child can remember at a time etc.  (level one) 3 animals, 1 shape, 1　action

Any music I played for my baby while she was in the womb, she loves now... even music in foreign languages!! I would also make sure you play music that you like listening to so you can have fun listening together after he/she is born.

Mommy of 1 from America living in Japan

It was very easy to install.

I think it would be nice if you could change the speed of the moving gifs. 

-Catherine