I'm suspecting newly hatched cockroaches.
I looked them up, and found this bit of information:
"A German cockroach is a white and extremely small right after newly hatched — almost too comparatively tiny to see with the naked human eye." The brown colors appear within hours of hatching, according to another article.
The egg cases may have come hidden in the corrugations of a cardboard box. I've had that happen twice in the last 7 years, but we were able to eradicate them successfully each time. Now I unpack all delivery boxes immediately and put the box outside my house until I can take it to be recycled. Sticky traps baited with peanut butter are safe to use if you have children and don't want poison in your house.
