Dog growls at son

Question
We went to adopt a rescued southern dog 10 mth-old shepherd mix last night. They couldn't tell me much background on why he was a rescue, that he was probably either wandering the streets as a lost stray or dumped at a shelter. He was shy but warmed up to me by lying down next to me of the floor where myself and my 6-year-old son were sitting, my 16 year-old daughter was nearby. He had been in foster care for a short time. They said he was ok with cats and their 6 year-old daughter. The transition here was fine, we slept without a peep all night in his crate and was happy to see my daughter this morning. When my son came into the kitchen, he growled briefly but did not show his teeth. My son left the kitchen a while later and came back within 10 minutes, he growled again, a little bit stronger. I placed myself between the two of them both times and just tried to re-assure the dog that my son was no threat. Now I'm wondering if I just agreed in dog language that he should growl at my son. I will have my son feed him tonight. Is there anything I should be doing or not doing? We really feel for him last night, I am just worried that I've bitten off more than I can chew?

Answer
Yes; Karre, this is the entire problem when you "Rescue" a dog...the term is just that!
I would be very hesitant right now not to get a second opinion from a Vet, or a top trainer in your area to see if this dog is sound enough for you to take on.
I fear he has had some real damage, and you could really be endangering your family.
The problem with Shepherds, is if they don't get "Real Socialization" from the get go, they are especially aggressive, and this will lead to "Fear biting" and other problems.
He could get trained over time, but, do you really want to live with this option in the meantime???
That is the point!
The real good dogs are not left in pounds and animal rescues, and if they were not cared for properly, chances are you as the "Good Samaritan" will only inherit those issues forever!!!
Try to search some Professional local help, and then make the decision!
Best regards, sorry for being tardy, was stuck in a "Snow storm"!
Regards,
Melissa