Ugh those turtles SHOULD NOT be kept as pets for the inexperienced!!

I'm assuming its a Red Eared Slider turtle, correct??

I REALLY hope they have it in at least a 25 gallon tank. They CAN NOT be kept in small fish bowls. They need room to swim, a basking light, a place to rest out of water, a hiding spot, a water heater, UVB light.....

And as hatchlings they are mostly carnivorous, so they can eat meat... try feeding him some meat if he isn't eating?? Also if you don't already get a UVB light, proper lighting helps them digest properly so if you don't have it that could be a problem too (if I recall correctly, its been over a year since I had mine)

I have a fanlisting here: http://dont-stay.com/res it also has information on RES about housing and nutrition

I hope the little guy is ok!!

edit: as a sidenote its ILLEGAL to purchase them under four inches in the United States unless its for research or educational purposes.. so that leads me to believe your mom got it from a very shady person who probably bred and sold them illegally!