You don't say how many children?
Would you have the time for a dog? I would advise against a puppy, they take up alot of time for house training etc. and can be injured easily if a toddler falls on them. A large dog can easily knock a child over when just walking around the house!
A dog takes up alot of time, just walking one two or three times a day for 20 mins (in winter when it is cold and wet). Then there is the feeding, water bowls constantly out around the house, kids playing in the water bowls etc.
If you do get a dog make sure it has a place it can escape to if it wishes, children playing can make any dog excited and hyper.
If you have more than one child under five I would imagine your time is pretty full! Might be worth waiting a couple of years until your children are a little older and you have more time available.
If you really are set on getting a dog a good rescue site to look at is:
http://www.freewebs.com/manytearsrescue/dogslo okingforhomes.htm