Before you start breeding gerbils, you must ensure that the environment they live in is safe for the potential pups.
Remove the wheel from the tank as well as any large or tall objects that the pups could get crushed under or fall off of.
The best tank for a breeding pair contains only the shavings, some cardboard to chew and some bedding for them to sleep in. Do not use the commercial beddings such as Hamster Fluff, because the fibers are long enough to wrap around a pup's foot or hand. This could potentially result in the amputation of the limb. For this same reason, you do not want to place fabric in the tank, such as towels or clothing. The best thing to use is shredded up facial or toilet tissue.
Also, make sure to use beddings that have a low dust and volatile oil content. Shavings made from cedar or pine should not be used because the oils in the wood can cause respiratory infections in the pups. I've heard that you shouldn't use corncob litter either because it is too dusty. The best beddings for a breeding pair are Carefresh litter and Aspen shavings. Aspen does not contain the volatile oils present in other shavings that can irritate the respiratory tract.
You will also want to avoid any other dusty materials like Chinchilla Dust. It is preferable to use Chinchilla Sand or play sand when there are pups in the tank. The pups are most susceptible to respiratory infections between the ages of 3 and 6 weeks.
Once the pups are a mobile, it is fine to give the parents back some of their smaller toys. When my pups were about 10 days old, I gave the mother back her coconut shell. You can see a picture of her to the right, very pregnant and happily chewing away at it. It is best to leave the wheel out of the tank until the pups' eyes are open.