Cool and dark
Though it doesn't promise that infant foxes were put in a sewer grate by their mother on purpose, animal specialists can think about a possible reason why she did so. Fox dens are cool and usually dark, so they are not unlike the sewage system grate where the babies remained in.
Mistake
When she left her babies behind while she went to pick up her den, it is possible that the mother fox made a mistake. The sewage system might be dark and cool, but its similarities to the usual fox dens were inadequate for it to be an excellent location for child foxes.
