Hi Kelly! I think YOU have to really decide if you want a dog. All kids pester for a dog at some point in their lives but they can lose interest quickly and, even if they love the dog, it will not be them who are doing housetraining, picking up poo, walking, taking to vets, sorting out holiday cover, wondering what to do with the dog when you want a full day out at Legoland etc etc. If you and your DH aren't that keen, it's really not a good idea. If you've got 3 children, you're probably already really busy with being a taxi for them, taking them to clubs, football, swimming, dr or dentist when required, friend's houses - does your lifestyle have enough time left to look after a dog??
Can you look after a friend's dog for a week or two, take some for a walk etc etc.
If you're thinking about a puppy, it's a full-time job, think hyperactive toddler who doesn't wear a nappy! They will poo, pee, chew, bite, need time invested in their training etc etc.
Not trying to put you off, but you really need to be realistic about the time you've got, the fact that you'll be doing all the work and that it's a 10-15 year commitment. 