My recommendation is rather than focus on any specific breed, you should begin researching pets available through local rescue organizations and find the dog that already displays the temperment and personality you seek. This is especially important with having such young children. This will give you an opportunity to "screen" and "interview" the dogs, so to speak before you make a final commitment. The folks that foster these pets will be able to assist you in identifying which dogs match your specifications. The bonus of going with a grown dog versus a pup is that you will not have to deal with the initial puppy training that is very time consuming and not always successful. With having twin toddlers on your hands, you want to keep the introduction of a dog into the family as simplified as possible. Good Luck!