Use Clump Curve

– Using clump curves you can have a better control on the way the children clump.
– When you enable the clump curve a graph appears with one starting and one ending point.

– To add a point: click on the curve
– To delete a point: select it and click on the X at the top right corner (but you cannot delete the ending points)
– To move a point: drag it

– X axis: position of the twists along the parent (0: root ; 1: tip)
– Y axis: distance from the parent (1= maximum distance, 0= minimum distance)

– I always find interesting to see how a child behaves when his parent is moving. In this video you can see two animations, note how the child firmly sticks to his parent when Y=0

– Another example:

Blender Hair Children Use Twist Curve