It kinda depends on the age of the kids.
They like the hair line, so I usually run my fingers through the hair and look for them.
I ask the kids to look in their groin. Otherwise I just do a quick visual inspection in places they can't see. If they are too old for me to be checking some of the places they can't see I teach them to use a mirror to check themselves.
Right now my kids are at an age where I am teaching them to check themselves, then double checking.
We check during bath at bedtime.