You have many threads about your hiv phobia, so should see a therapist who might be able to help you live a normal life instead of thinking hiv is everywhere and going to infect someone from toothpaste. Since you had so much advice before, I will say your idea of toothpaste infection is silly.
Your son would not be at risk from sharing toothpaste or toothbrushes with you. As you have likely been told, HIV is spread through unprotected vaginal sex or anal sex or sharing IV drug needles. Saliva inactivates the virus. Air does as well. A toothbrush would not transmit HIV. Objects do not transmit HIV. Your son is fine.