It's true that you can't 100% trust your family members, relatives, family friends, etc.  

Some people are mentally deranged, sex obsessed, sexually repressed, shy, socially awkward or abnormal, ranting & raving lunatics (also known as narcissists) and they will try to have sex with ANYBODY - example: family members, siblings (brother or sister), relatives, kids or teenagers of family friends, etc. 

The sexual predator / molester can be male or female, of any age: young kid, teenager, adult, old person, etc. Gay, straight, lesbian sexual predator / molester.

Watch over your kids. Even when the kids become adult, the adults are not safe. The sexual predator is obsessed with sex with ANYBODY.