Not long ago friends of ours made an impulse buy of a cute puppy, and they're now dealing with the aftermath of that decision. With that in mind, I have a few thoughts for you to consider.

Side note: We have a family dog, tastefully named "Max", so I also have personal experience as a dog owner.

My list:
1. If you're getting a purebred dog, try to match the breed's size and temperament to your family. If it's a mixed breed, look at its heritage (if known) to get a rough idea of how the dog will behave as it grows up. Our Max is a funny-looking retriever/terrier mix adopted from a shelter, and we looked at quite a few puppies before choosing him, but his personality and activity level match our family well. High-energy dogs require more exercise and attention, and kid-friendly is a must for you. I'm no expert, but I'd predict a lab/beagle mix would be fairly large and need lots of exercise.

2. Puppies grow up into dogs. Our friends got a cute female Weimaraner puppy, and Belle is rapidly growing into her full size, which they estimate to be somewhere between a rhino and an elephant. Other friends got a cute chocolate Labrador retriever puppy, and Hershey now weighs 120 pounds and is ridden like a horse by their daughter. All puppies start out small, so make sure you consider the final size of the dog.

3. Housebreaking a dog requires patience and lots of time outside, and the best time to teach a dog that skill is when the weather is good as someone will be waiting outside several times a day for the dog to do its business. If puppy time is now, you should be good to go on this one.

4. Dogs are a lot of work, and it's essential to have clear expectations of who will handle which chores. Though it's a good idea in theory to put little kids in charge of feeding the dog or filling the water bowl, you will have a hungry, thirsty dog if there isn't an adult backup. Whenever I go on a business trip, I tease Max and tell him to stuff himself and drink a lot before I leave, as it'll be slim pickings while I'm gone.

5. There is an adjustment period for everyone when you bring a puppy home. The first month with Max was rocky and stressful, but once he was housebroken and understood basic obedience concepts, things got better in a hurry. Expect to have some rough patches soon after the puppy arrives, with the most likely culprit being frequent pooping or peeing inside the house (and sometimes it happens five minutes after you just spent an hour outside watching the dog scratch itself, chase dandelions, and do a zillion other things without relieving itself).

6. Dogs are great pets. Max can be a giant pain in the arse at times, but overall he adds a lot to the family and we'd all miss the oversized rodent if anything happened to him.

Good luck!