I think this topic is very prone to being one over arguing the definition of what we mean when we say "jealous" rather than whether or not dogs are capable of the emotion. We may very well have to redefine the word itself to include non-human behavior types.
I don't know whether or not dogs can actually display jealousy, but I do know that dogs are pack animals that always seek to establish a pecking order.
Having one dog and adopting another is one thing, but just wait until you have a breed of dog that tends to be dominant to begin with, and then you have a kid. More often than not there WILL be issues if the dog is not made to understand that your kid is your offspring and comes first before your dog no matter what. That will lead to said dog to display aggression towards the child.
Our Westie tends to be dominant when there are other dogs around, and she CONSTANTLY tests the limit around my kid. For example when I come home and my kid runs to me, she will try the damndest to "be more cute" than the kid so that I give her more attention. Consistency is key, so I always push her aside to wait for her turn, as second.
I regard jealousy to generally be "the negative thoughts and feelings of insecurity, fear, and anxiety over an anticipated loss of something of great personal value, particularly in reference to a human connection" as outlined by Wikipedia. I realize there are many variations out there.
By that definition I would say that the dog does not display jealousy but rather dominance.