I grow a fluffy beard but have no mouth,
No shield but stand in a phalanx with my kin,
Guarding the road of roads,
I am so weak a child can slay me,
Yet I can lift men and heavy stones,
Who am I?
Answer:
A reed.
Note on clues:
Line 1: Reeds have little hairs that grow to disperse their seeds through wind. Quite distinctive when you've seen them, like a less extreme version of cattails.
Line 2: Reeds grow in thick clumps all standing straight, pretty self-explanatory.
Line 3: "The Road of Roads" is a kenning for river which is
in the riddles Odin gives to King Heidrik.
Line 4: A reed can be broken by a child.
Line 5: Reed baskets and reed boats go back centuries and would be known to the Norse as they were to most Eurasian cultures.