how can I turn, "The children were nestled all snug in their beds, while visions of sugarplums danced in their heads; and momma in her kerchief, and I in my cap, had just settled down for a long winter's nap" into informal writing

The answer is:

The children were lying warmly and tightly in bed, while they were having sweet dreams; and momma in her bandana, and I in my cap, had just got ready to take a long winter's nap.

An informal register is used when speaking or writing to people we know well, like family and friends. There are no considerable rules in informal language, so it is appropriate to tell jokes and the use of slang, contractions, personal opinions, incomplete sentences and extra punctuation.