On the growl at the other dog, I mostly only worry if they growl at humans trying to move them from their space. If he is new to that home it is normal for him to still be working out the pack dynamics with the dogs in the foster home.
Take him for a walk outside when you meet him before you take him in your home. don't let your kids mug or rush him but give him plenty of time and space. Tell the kids, new dogs are best left alone at first and let him have space to find his way if you get him. He needs to reach to you.. not the opposite. Some reach right away, some need a few minutes to warm up.
I adopted a dog once and I was showing her to my mom. She was an abuse case. My mother after hearing her story dropped to her knees and hugged the dog around the neck hard. My dog screamed in fear and pulled back hard hitting my mom in the cheek with her head. My mom told everybody my dog "turned on her". I worked and aclimated my dog to being held and restrained and she never bit anybody in her whole life and was a terrific dog. Human fault, dog was blamed. Just be very observant and gentle slow body language. he will tell you if he is supposed to be your dog. You will feel it. Any reservations whatsoever, and you should pass on him given that you have small children in your house. Might be worth taking somebody else with you to see him to see how he is with other folks. best wishes.