When telling a child about putting a family dog to sleep, explain that the vet can't do anything else to make the pet better. Use clear terms based on your child's age to let the child know the dog will not come back. Avoid using the term "put to sleep," because it may cause the child to fear falling asleep.
The key to talking to your child about pet euthanasia is being sensitive to his thoughts and using words he understands. If your child has experience with death or is old enough to understand dying, use those terms during the discussion. Explain that the vet gives the dog a shot so it won't feel any pain before giving it medicine to stop its heart. Let him know putting the dog to sleep is the humane thing to do because of the health problems of the pet.
Listen to your child if he wants to talk about the process. Let him ask questions, and answer them as honestly as possible within his scope of understanding. Your child may continue to have questions even after the pet dies.
Another question parents often have is whether or not to take a child along for the euthanasia process. Consult with the vet to determine if children are allowed in the room. Determine if you think your child can handle seeing the dog die.