Each aquarist has their favorite fish. I suggest going to the aquarium store and writing down the names of the fish that you like. Don't buy any yet. Then, research those fish and see if they are compatible with your fish. The guppies, platies, and pleco would do fine with many docile community fish such as most danios, white cloud mountain minnows, corydoras catfish, docile barbs, docile tetras, and so on. The guppies and platies like water a bit harder and with more salt then the pleco and the other fish that I mentioned.
The "shark" that your daughter saw was probably one of the catfish (since it had whiskers) and not the cyprinid "sharks."
It might be one of these species:
http://www.planetcatfish.com/catelog/speci...?species_id=276http://www.planetcatfish.com/catelog/speci...?species_id=700I don't really suggest any of the freshwater fish called "sharks" for community tanks with small fish because they all grow large and can eat smaller fish.
How did you explain why mommy guppy ate the baby?