Those five words you don’t want to hear: “Mom, we want a puppy!”

You know you don’t have time in your busy life for a dog. So you promise the kids they can have something small and furry instead.

But if you want to teach your children that a living thing is a commitment for the pet’s lifetime, make sure you know what you’re getting into.

“Do your research,” says John Tarrant, co-owner of Outragehisss… Pets in Chestnut Ridge, N.Y. “There’s no such thing as an easy pet. Some are easier than others. I never use the word ‘easy.'”

Tarrant knows his animals: His collection ranges from tarantulas to two-toed sloths. And he knows children, too: He runs scores of animal-themed birthday parties and wildlife education programs every year.

Remember, as Tarrant says, “If it sounds too easy, it’s not true.”

Gerbils are probably among the lower-maintenance pets – they make less of a smell than mice or hamsters, he says.

As desert animals, they use water efficiently, producing little urine and relatively dry stool. They also are relatively handleable.

“A lot of hamsters do nip, and it doesn’t take much to pierce a kid’s finger,” he says.

If you’re looking for a slightly larger pet, guinea pigs are charming, and come in many interesting coat and color variations.

But Tarrant warns that they can be more work. They eat and drink more, with predictable results. “The biggest complaint I hear is, ‘I didn’t realize they were going to be so messy,”‘ he says.

Whatever you decide to choose, keep in mind some general rules.

For example, don’t forget that your child’s interests may shift with age. Tarrant suggests that you pick animals that are “not as long-lived – not as long a commitment.”

A gerbil that lives two-to-four years may be a more reasonable choice than a chinchilla that could still be around when your 6-year-old is ready for college.

Do your research before buying your supplies, as well. If you’re well-informed to start, you’re better able to judge the quality of the advice you’re getting at your local pet store.

“Food with nuts and seeds in it will cause guinea pigs to choke,” says 16-year-old Grace Spring, who runs Furry Friends Guinea Pig Rescue in Wallingford, Pa.

“And an important part of a guinea pig’s diet is fresh fruits and vegetables. A lot of the time you don’t get informed about that,” she says.

And rather than buying your new pet, consider adopting from a shelter or a rescue group. Rescues will provide detailed information on both the species and the individual animal.

“You’ll know the history of the animal you’re adopting from a rescue, which you’ll never know from a pet store,” says Spring. “You know all the health issues beforehand.”