Option A: In the given sentence, the nouns 'children' and 'fathers' are plural. So, there should be a consistency in terms of number in a sentence. The phrase 'a farmer' is singular, it refers to only one farmer, whereas 'fathers' is plural. Hence this phrase must be changed and option A is incorrect.
Option B: 'Agriculturists' is a plural noun and agrees with the rest of the sentence, by referring to the fathers of many children. Hence B is the right answer.
Options C and D: In these options too, 'a forester' and 'a woodsman' is singular and does not agree with the sentence. Hence C and D are also wrong.