What you may not know is that many breeds today have very small populations. If some breeds were any other kind of animal they would be considered endangered. You may find it hard to believe, but breeds can become extinct. If you read any histories about dog breeds, you will find lots of references to breeds that are gone now. Countless breeds have become extinct over the centuries. In some cases we have some of their descendants because they contributed to newer breeds, but not always. Some people might not care if particular breeds become extinct, but if you are a fan of a breed, then this might matter to you. From a genetic viewpoint, it’s always good to have a wide selection of dogs that contributed to a breed’s foundation. You never know when it might be necessary to reintroduce some of the genes from an older breed for health reasons. If those breeds are extinct, that’s no longer a possibility.
Most all dogs will get along well with children if they are raised with them. However, some breeds have a protective streak in them and may become aggressive with children who get to close at meal time (although this should not be tolerated), or aggressive with children they have never met. These breeds will likely see the children as being underneath themselves in the "pack order" and may try to dominate them.
Your dogs temperament should match yours. Do not choose a breed that is highly energetic if you are a couch potato. On the other hand, if you want a dog that will follow you everywhere around the house and who is always ready for a game of fetch or tug of war then you should consider a dog that is highly active and always has a lot of energy, instead of one of the lethargic breeds.
Some breeds have so much energy and are so active that if you do not give them a sufficient workout every day - a long walk and hard run - their pent up energy will quite likely manifest itself in destructive behavior.