To what does the speaker in Longfellow's poem, "The Children's Hour," compare the children, & what words or phases sustain the metaphor?

In this light and playful poem by Longfellow, the poetic
speaker compares the children, "Grave Alice, and laughing Allegra, / And Edith with
golden hair," in an implied metaphor, to an ambushing army storming a castle. He
underscores this metaphor through an allusion to an old oral tradition folk tale called
"The Mouse Tower," which features "the Bishop of Bingen / In his Mouse-Tower on the
Rhine!" The Bishop was besieged by hungry town's people who repeatedly begged for wheat
from his granaries to feed their children during a time of failed crops following the
flooding of the Rhine River.

In this dark folktale (making it a
surprising allusion for Longfellow's playful poem), the Bishop flatly refuses to aid
them, which results in a tragedy that ends with his being ambushed by a vicious army of
devouring rats. Longfellow inverts the intention of this devouring army when he says of
the girls that "They devour [him] with kisses."

The words and phrases
that sustain Longfellow's metaphor are many and liberally sprinkled throughout the poem.
Some of these are: surprise, indicating ambush;
raid, indicating army; castle wall, indicating
assault. Others are:

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plotting and planning
doors left
unguarded
enter castle wall
climb up into my
turret
escape
surround me
O blue-eyed
banditti
scaled the wall
fast in my fortress
down in the
dungeon
the round-tower
Till the walls shall crumble to
ruin.