What is the best breed of dog to get for small children (7, 3 and a baby) also is it better to rescue an older dog?

I am considering getting a dog for my children and would like to know which breeds are good for small children. I am interested in small to medium-sized dog. We have a large yard and someone will be home most of the day every day for the dog. We would like the dog to be mostly an indoor dog, but need one with a laid back temperament for the kids. Also, what are the advantages or disadvantages of getting an adult dog verses a puppy?