I've wormed both my kids as we have a lot of animals they interact with, they play in the dirt a lot and go to school. From my understanding basically intestinal worms shed their eggs in poo and they will also gather around the anus, so scrathy = exposure to eggs if that hand goes anywhere near the mouth, or anyone elses mouth.

I wouldn't say I do it regularly but probably at least 1-2 times a year if I notice itchy bottoms, loss of weight (easy on my son who eats barely anything), sore tummy etc. We use the chocolate squares from the chemist for the whole family, it's such a treat sharing dessert together lol. wash all bed linen and clothing and hang in the sun