Most dogs are naturally enthusiastic about food and may nip at your fingers when you offer them something. It is important to teach your dog to take food gently so that you and others may safely offer your dog food in response to good behavior and for the purpose of socialization. This is especially true for children. Your dog will make fast friends with children if they can offer him tasty treats from their hands.
If your dog takes food roughly, do not give him the food. Take your hand away and then bring it back to give your dog another chance to get the food. If he is more gentle the second time, open your hand and give him the treat. If not, take your hand away again. It may take many repetitions before your dog begins to understand how to get the food, but actions speak louder than words. So stay quiet and let your dog figure this out for himself. It may be helpful to have your dog on leash and tethered to a stable object so that you have both hands free and can stay just out of your dog’s reach should you want to step away and give him a time-out from training.
You can also simply keep your hand still and closed around the bit of food that you offer to your dog. He will probably try to get the food out of your hand by mouthing it and pawing. By keeping your hand closed and still, you are telling your dog (without words) what doesn’t work. He will eventually stop doing the behaviors that didn’t work and pull back, at which point you should open your hand and give him the food. Repeat until he automatically backs off and waits for you to open your hand and offer him the treat. By doing so, he is showing you that he can control his impulses and be thoughtful and careful when accepting food.