Final answer:
The riddle plays on the word 'dad' as Timmy's son is figuratively the 'dad' to his dog, which makes him the 'granddad' when the dog has puppies.
Step-by-step explanation:
The question seems to pose a riddle rather than being related to an academic subject. It playfully challenges the reader to reconcile how Timmy's son could be a dad if his 'child' is a dog that has three kids. The key to solving this riddle is recognizing that the term 'dad' is being used figuratively. Timmy's son is referred to as the 'dad' of the dog, meaning he is the dog's owner. Consequently, when the dog has three 'kids', or puppies, it makes the owner (Timmy's son) the 'granddad' in a whimsical sense to the puppies.