The very first filter I used when I started the hobby several years ago was in a clear plastic box. It was a cube about 3 inches in each direction that held carbon and filter floss. In the center was a tube that came from an air pump to get some water movement. I'm not sure what this filter is called, but it would be awesome for fry.
You could also just use the regular penguin type filters if you clog the intake with a sponge. If you get it just right, there will still be water getting sucked in, but it won't take the fry too.