Ivermectin not recommended below 5 yrs. Also it's not the best drug for pinworm. Other drugs useful are Mebendazole and Pyrantel palmoate
Next Steps
May take a week to clear all worms. Some of these may be dead worms Albendazole needs to be repeated after 2 weeks of 1st dose
Health Tips
Rinsing area well, good hand hygiene, treatment of family contacts will prevent re infection