System Information
Operating system: Linux-5.4.0-90-generic-x86_64-with-glibc2.27 64 Bits
Graphics card: GeForce GTX 1660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.91.03

Blender Version
Broken: version: 2.93.5, branch: master, commit date: 2021-10-05 12:04, hash: rBa791bdabd0b2
Worked: unknown

Short description of error
If you use particle childs and set an "particlesettings.child_radius" to spread them out without setting "particlesettings.child_roundness" i get the straight lines in the render as seen in the example.

By creating a new file to reproduce / investigate i see that the childs are created in an plain circle. I expected an cube. So it maybe just needs a better label / description.
Maybe improve the function with an option for base geometry like cube, sphere, plane, circle, line. etc, would improve usability for some effects.

Exact steps for others to reproduce the problem
Create a new file with a plan that is emmitting particles with childs.
Set the childs radius to an value > 0.
Leave childs roundness to 0.
With camera angles parallel to the y-axis of the emitter you see no distribution due to plain circle.