Who can touch my private parts and why is it not OK to let anyone touch my private parts?
As a kid, you are normally dependent on your parents or your caretaker for the day-to-day activities like taking bath, dressing up, etc. In such cases, it is perfectly fine for your parents or caretaker, especially mom, to touch your private parts. Similarly, whenever you are not feeling well and hence taken to the doctor, the doctor can be allowed to touch your private part, provided your mom or dad is along with you.
Otherwise, nobody else is allowed to touch them, since it is your private part. The reason for not allowing others to touch your private part is that you are not aware of how healthy and clean they are. The private parts are very sensitive and can easily contract infections. Your parents will always double check the cleanliness before they touch yours, because they care about you. But we cannot expect the same from others. Also, there are some bad people, who can exploit our private part and hurt them. Hence, it is not necessary to allow any other people to touch your private parts.