Make sure that the gerbil food you are giving them isn't too high in fat. The bird-seed type mixes may be tasty to them, but they are like eating lard for every meal. I give my gerbil large, ra t pellets that are about the size of two keys on your keyboard. For treats I give her sunflower seed, peanuts, and granola. I also treat her with cereal such as kix or cheereos.
Exercise is very manditory for a gerbil.
Sometime I let my gerbil run around loose in my room . The dangers of that is make sure the room is closed up, always watch so it doesn't chew the electrical wires, and don't step on them. They move fast and you might find them inder your feet before you know it. It is also important that they always have cardboard in their cage to chew. Their teeth are always growing and the teeth will get too long if they can't chew on something.