It could mean that his mom wanted to care for Jack's injury with the materials that she had available.
Or, it could be a political or social commentary. When nursery rhymes originated, most people did not read and write, and books and newspapers were of little use to them. However, people were very clever. They made up rhymes to say to their young children which were really a way to avoid trouble with authorities or the better social classes while voicing their distrust, disgust, or other negative opinions of them. This is the reason that some nursery rhymes may not seem child friendly.
"Jack fell down and broke his crown". Crown is another word for head.
"... wrapped his head in vinegar and brown paper."
Possibly from Jack and Jill..He went to bed to mend his head with vinegar and brown paper
Jack laughed at Jill because she mocked him when his head was bandaged in vinegar and brown paper, knowing that she would face a similar fate for laughing at him. It was a moment of irony and comeuppance for Jill.
Your mom would have fixed your head injury with vinegar and brown paper by applying it gently on affected areas.
It is a tit-tat game between Jack and Jill. What goes around comes around
The pH paper (Merck art. 9565) become brown.
His crown refers to his head. His mother fixed it with vinegar and brown paper.
Red litmus paper dipped in vinegar will turn red, indicating that vinegar is acidic. This change in color is due to the red litmus paper reacting with the acidity of the vinegar, causing it to remain red. Litmus paper is commonly used to test the acidity or basicity of a solution by observing the color change it undergoes.
pH paper will turn red when put in vinegar, indicating that vinegar is acidic.
If if it is red Litmus paper, then it will remain red because vinegar is acidic. (Blue Litmus paper would turn red if you dipped it into vinegar).
If the vinegar is strong enough to be below 4.5 pH the litmus paper will turn (or stay) red.