Final answer:
The sentence is a simple sentence because it contains only one independent clause and no subordinate clauses.
Step-by-step explanation:
The sentence in question, "On the day of his birthday, his mom made his favorite breakfast," is an example of a simple sentence. A simple sentence, also known as an independent clause, contains a subject and a predicate and expresses a complete thought. There are no subordinate clauses or additional main clauses that would characterize it as compound, complex, or compound-complex.