My son and I kept a red ear for four years until a heater mishap.
Having raised our turtle from that size to around 10 inches long I can say from personal experience that I would not do it. These guys eat anything and everything. They are little garbage disposals in a shell. I would not be at all surprised to find out they would, even at that size, attempt to eat a firebelly toad.
We fed our guy a huge variety of food. Turtle food, grubs, worms, and feeder fish. These guys are fun to own though all on their own and I really would like to get another one eventually.
Just as a tip to help you avoid our little tragedy; change out your water heater once a year as recommended. Our heater was over two years old and malfunctioned which overheated our little guys water while we were away. A heater isn't really necessary if you'd like to play it safe but it's for their comfort.
One last note on these little guys is they grow to be very waste productive. You'll need a filter that cycles your water capacity at least five times per hour.
That's my two cents.
They are a lot of fun to own and I'm eager to get another. Feel free to hit me up if you have any other questions. Take care!