Been there and done that!! The reason I got into fishkeeping was because of my kids! I had to fish-sit and that was the beginning of this for me. Now I love it more than the kids.
My suggestions for a 2 gallon would be no more than 3 zebra danio. They are very active fish that can live through MANY water conditions, and do not require (although prefer) a heater. They do sell small heater for tiny tanks. I have a 3 gallon for my son with danios and I bought the smallest heater I could find and it's on a very low setting. Just get a thermometer and make sure you start low and slow should you decide to heat the tank.
Here are my two favorite links for starting an aquarium. They helped me more than anything when I first started. I also highly recommend BioSpira, which is mentioned in the article. I use it all time and it has worked wonders.
Enjoy your new hobby! I bet you'll eventually realize that you got the last laugh with your mom! : )[/url]