Reply To: Child hair particles turned wrong way through mesh

That seems to be, because of the way Blender calculates the interpolation of the Child Hairs. With only one Hair:we get:

But with more Hairs:

we get:

Not only do some Hairs go through the Mesh, but some Hairs are also shorter!

Apparently Blender considers a Hair going in opposite (World) direction to have an opposite (negative) length…

I’d call this a bug, but the system is going to be replaced/overhauled anyway (if I understand correctly). 

It’s not some kind of Setting that you can change, you didn’t do anything wrong.

What you could do, is to not use Children, simply more Parents…

Or use two Particle systems, one for each side….you can use strips that you Shrinkwrap to each side as Emitters.