A beggar with two children ____ taking a rest in the shade. (be)

In the sentence, the subject is 'a beggar'. 'Two children' is not the sucbject of this sentence. Bracket 'with two children'. Then you can notice that you have to use a singular auxiliary verb 'is' in the blank. Don't forget that a singular subject takes a singular verb. Also don't forget that you should ignore the words between the subject and the verb.

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Thank you for your help. With your correction, I can know suitable expressions. I appreciate your help.
I have posted an example sentence and the explanation about that. Are the sentences grammatical? If you find any errors, correct them, please.

All looks good except for one punctuation error, which shows up twice. A period or comma needs to come before the closing quotation mark -- 'a beggar.' and 'children.'

http://owl.english.purdue.edu/handouts/grammar/g_quote.html
Scroll down to Punctuation with Quotation Marks for the full explanation.

Of course, you can avoid this punctuation issue completely by putting those words in italics instead of quotation marks!

Your sentences are fine; they read very smoothly.

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Thank you. Can we say as follows?

Parenthesize 'with two children', and find the verb suitable for the subject.

It would be better to say it this way:

Put 'with two children' in parentheses, and find the verb that agrees with the subject.

Making sure the subject and verb match in number (singular or plural) is called subject-verb agreement. Using the word suitable implies being suitable in meaning, whereas agrees with specifically means using singular or plural form correctly.

There is a verb parenthesize in the dictionary, but it's not often used.
http://www.answers.com/parenthesize

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Thank you for your kind words! I'm glad I could help. The corrected sentence "A beggar with two children is taking a rest in the shade," is grammatically correct. It follows the rule that a singular subject (in this case, "a beggar") takes a singular verb ("is"). The phrase "with two children" is a prepositional phrase that does not affect the subject-verb agreement.

Your gratitude is appreciated, and I'm always here to help if you have any more questions or need further explanations!