There are some parts of M, both in form and in content, that can only be explained by the time and place of its production. A child murdered would not fit easily as a subject not even in contemporary films (cannibals seem to be okay nowadays, but child murderers are not so prominent).
Early 30s was a time of disillusionment for Germany which lived the last days of the Weimar republic just before the ascend of the nazis to power a couple of years later. The main theme of the film is not the specific target of the murderer (Lang only needed something atrocious) but the general feeling of inse