What are the symptoms of pertussis in a toddler?

See below: Pertussis begins with mild respiratory symptoms similar to common cold (catarrhal stage), followed by paroxysmal stage characterized by paroxysmal cough and whoop often followed by vomiting. This stage often lasts 6 to 8 weeks. Severe cough spell and apnea (cessation of breathing) especially in young children can result in rectal prolapse, subconjunctival hemorrhage, and seizure.