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I don't like to recommend breeds for outside dogs because it never seems to work out the way the owner think it will. Outside dogs who do not have a full-time job (livestock guard dogs, etc.) tend to be substantially more badly behaved than inside dogs, no matter what breed. They never have to learn their manners and when they do get inside they go crazy with the joy of it and so, of course, somebody yells to throw the dog outside again. This would be especially true for a dog intended for a little boy; as soon as your son goes outside he's going to get a flying tackle by a dog who hasn't seen him in hours. No dog - and I really mean NO dog, unless it's terribly elderly - just happily walks around outside sniffing things and enjoying being in a small yard, and then gracefully and calmly greets their family when the humans come out. They either create their own job - digging, barking, chewing, chasing things - or they fight to get inside where their people are. Dogs are so intensely pack animals that without company they go a little bonkers when they can't get to them. 
If you're willing to consider a real family dog - one that will be wherever you are, whether inside or outside - there are a few breeds that seem to always do well and are handily sized, but don't have so much prey drive that they'll be a danger to your chickens. Boston Terriers are a classic. A WELL-BRED miniature (not toy) poodle is fantastic (just, please, do not try to save money on a poodle - the breed is riddled with issues and the badly bred minis have awful, AWFUL temperaments right now). I have Cardigan Welsh Corgis (25-35 lb) with four kids and, while they need to be supervised with the birds or they'll herd them for hours and tire the chickens out, they're very gentle and good with even the baby chicks. Don't get a terrier, a sporting breed of any kind, or a hound. All of those will kill your chickens. I'd recommend against the big herding dogs as well; they have too much drive for most families and you can never meet their exercise needs. Look at the medium-sized dogs in non-sporting group, the small herders, the large toys. Those tend to be good candidates for family dogs because that's what they've been bred for deliberately.