Could the second dose of Bexsero have caused a slight strabismus in the child?

Any health disorder may or may not be the result of a drug/dietary supplement/vaccine. However, the manufacturer of the Bexsero vaccine does not mention among the possible side effects disorders within the visual apparatus. If you are concerned about the occurrence of such a symptom, you should report it to the attending physician. Based on physical examination and other factors (m.in time after vaccination), he will determine the probable cause of the problem. I also encourage you to read the article on reporting side effects of drugs: https://www.gdziepolek.pl/artykuly/jak-i-dlaczego-zglaszac-dzialania-niepozadane as well as on preventive vaccination in children: https://www.gdziepolek.pl/artykuly/kalendarz-szczepien-dla-dzieci-i-niemowlat