Consider your kids' ages, temperaments, and activity levels, as well as your own lifestyle:

Active children may do better with a mellow dog who won't get overly excited along with your child.

Herding breeds are a poor choice in households with young children, as are small, delicate dogs like dachshunds and Yorkies.

How much time will the dog will be alone, either because no one is home or because all your attention is on your preschooler (such as potty-training time)? Some breeds can be alone more than others.

Size and appearance don't determine temperament: A Jack Russell terrier needs as much exercise as a Border collie, but mastiffs and greyhounds tend to be big couch potatoes.

Consult a trainer to help you decide what type of dog would be best for your family.

If a puppy sounds like too much work, consider adopting an adult dog. There are millions of wonderful dogs that pass through shelters every year, and there's a good chance they're already house-trained and done with their chewing stage.

To house-train your pup, you'll need to take him out on a leash several times a day--even if you have a fenced-in backyard; he needs you to tell him he went in the right place (outside!).

Puppies need lots of playtime and socialization with humans and other dogs. Plan to play with your puppy at least 20 minutes three times a day. Also take him to the park, walk him past schoolyards, and take him to a puppy playgroup.

Sign up for training as soon as your vet says your puppy is ready. Be sure all family members--even preschoolers--are involved. Practice for five minutes, three to four times each day at least until age 1.

The first year of a puppy's life is the most expensive. You'll pay for:

Vet visits--For booster shots (three rounds), spaying or neutering, and both a heartworm preventative and a flea and tick preventative. Vet costs for your puppy's first year can range from $300 in rural areas to $600 in bigger cities.

Initial supplies--These could cost from $200 to $400. Large items (crate, bowls, and collar) for large dogs cost more than items for a small dog. See the new-puppy checklist.

Training--It's essential, especially with small children at home. A basic obedience group class can cost from $80 to $350 depending on where you live.

Puppy food--A high-quality dry food for a dog under 20 pounds can cost as little as $10 per month. The same food will cost $40 a month for a large dog. Wet food and specialty foods cost significantly more. Remember to factor in bones and other treats.

Boarding fees--Your pet will need either a sitter or a kennel during family vacations and trips to grandma's house. Depending on where you live, overnight boarding can range from $20 to $60.

Exposed wires and toxic plants can be a big danger to a curious pup.

Rugs are just big wee-wee pads! Pick them up until your dog is fully house-trained.

Put away anything that smells like food (the recycling bin) or smells like humans (shoes, remote controls, cell phones).

Explain to your children that dogs don't understand the difference between their own toys and kids' toys. Encourage preschoolers to pick up toys after they play, especially small toy parts that could be easily swallowed.

Everybody needs to reinforce the same rules. Is the dog allowed on the couch? On the beds? Will he be fed food from the table? Where will he stay while we're not home?

Children should agree to additional--and very important--rules: no teasing, tail-pulling, running, chasing, or yelling at the dog, and certainly no hitting.

Sit down together and work out a schedule for house-training duty, exercise duty, and obedience training that involves every family member. Small children can help even if they can't be responsible for these tasks.

Place both the house rules and Nick Jr.'s Puppy Chore Chart on the refrigerator so everybody knows what they are expected to do.