I think that is, because you are using interpolated children (which is correct).
Suppose you have only two hairs, one on the left side of the head and one on the right, then an interpolated child will be somewhere in between and might end up coming out of an eye;)


This will get better if you have more hairs.
It can also be improved, by making more ‘scalps’, one for the left side, one for the right and maybe even a top and back one…