I had them once when I was little.
My children have had them twice. Once when ds1 was two and dd was only about 6 weeks old. I rang the doctor about dd who said it can't be possible for her to have them as they have some sort of immunity to them, but she did! Couldn't use any treatments on her so wet-combed daily to get rid of them.
Second time all three children got them about a year ago. Tried a £10-a-bottle treatment which didn't work, so wet-combed again and have at least once a week since, as it was such a nightmare! Also check my own hair every other day as I always have an itchy head and am convinced I have them, but never find anything!
Surely it is neglect not to treat them?!