Son cannot afford-Raising money and getting a job to support parents who cannot afford:[1]

If the child cannot afford to feed his parents from his own money, then he is not obligated to beg for money [or get a job[2]] in order to feed his father. [Likewise, if the child cannot afford it, then he is not required to use his own money and food to feed them and support them, and then have to go begging for money [or get another job] to support himself.[3] However, if one in any event collects money from others on behalf of himself then some write that he must also collect money on behalf of his parent.[4] However, other Poskim[5] negate this obligation and rule that one is never obligated to go begging to collect money on behalf of his parents. Whatever the case, it is certainly a mitzvah to raise money on behalf of one’s parents even if he is not obligated to do so, and one may do so even if he is a Torah scholar who generally views it as below his dignity to do so.[6] This especially applies if otherwise the parent will need to go out begging on their own.[7]]

Definition of “can’t afford”: As stated above in B, one is only required to support his parents in accordance to his charity obligations, and hence if due to his poor state he is not obligated in charity then he is likewise not obligated to support his parents. [However, some Poskim[8] rule that in this regard we follow whatever is accustomed in society for one to support his parents even when he is poor, and do not abide by the regular laws of affordability regarding regular charity. Furthermore, some Poskim[9] rule that the definition of lack of affordability in this case is if the child does not have enough money to support himself for 30 days, in which case he is exempt from supporting his parents. Other Poskim[10] rule that the definition of lack of affordability is if the child does not have enough money to support himself and his household for one full day. If, however, he has enough money to support himself for one full day then he must give the remaining monies to support his parents.]

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[1] Michaber ibid; Tur 240:5, based on Rosh ibid based on Yerushalmi Kiddushin 1:7; Ran Kiddushin 13b; Rabbeinu Shimshon Peiah 1:1; Hagahos Maimanis Mamrim 6 Os Daled; Semag Asei 112-113; Bach 240 according to Semag and Semak that this applies even according to Poskim of Shel Av; See Poskim in Encyclopedia Talmudit ibid footnote 348-355

Other opinions: Some Poskim rule that a child is obligated to even go begging for money for the sake of supporting his parents. [Rashbi in Yerushalmi Kiddushin 1:7, brought in Tosafus Kiddushin 32a and many Rishonim and Poskim brought in Encyclopedia Talmudit ibid footnote 329 and 332 and 336 that is Rabbinical; Chinuch Mitzvah 33; Sefer Hachareidim Asei 5:1] Alternatively, he must get a job for the sake of supporting his parents. [Semak; Semag; Kad Hakemach; Brought in Bach 240; Encyclopedia Talmudit ibid footnote 338-342]

[2] Setimas Haposkim ibid; Bach 240; Encyclopedia Talmudit ibid footnote 354-355

Other opinions: Some Poskim rule that a child is obligated to get a job for the sake of supporting his parents. [Semak; Semag; Kad Hakemach; Bach ibid according to opinion of Shel Ben; Poskim Encyclopedia Talmudit ibid footnote 338-342] Some Poskim learn that this obligation according to these Poskim applies even though he is not obligated to go begging for money. [Bach 240; Encyclopedia Talmudit ibid footnote 341-342]

[3] Shach 240:5; Bach 240; Rosh Kiddushin 1:50; Poskim in Encyclopedia Talmudit ibid footnote 351

The reason: As one is not required to shame himself on behalf of his parents if the shameful activity does not contain any intrinsic honor first parents. [Bach ibid]

Other opinions: Some Poskim rule that a child is obligated to support his parents with his own money even if it means that he will have to go begging for money for the sake of supporting himself. [Chayeh Adam 67:12 in name of some Poskim; Poskim in Encyclopedia Talmudit ibid footnote 337 and 343 and 349] Some Poskim argue on the above and rule that indeed he is obligated to go begging for money either on his own behalf or on behalf of his father and it is his choice to choose whether to give his money to his father and then go beg for himself or to keep his money for himself and go beg for his father. [Chazon Ish Kiddushin 32a; See Even Yisrael Kiddushin ibid]

[4] Avnei Zikaron p. 303

[5] Imrei Yosher 2:180; Shevet Halevi 2:111-3; Rishonim and Poskim in Encyclopedia Talmudit ibid footnote 348

[6] Ben Ish Chaiy Shoftim 2:8; Nishmas Kol Chaiy 1:57; Pada Es Avraham Mareches Chaf 1

[7] Ben Ish Chaiy Shoftim 2:8; Aruch Hashulchan 240:22 regarding one’s mother; See Kesubos 67a

[8] See Radbaz 2:663 “Although we take from the son under the category of charity, nonetheless it doesn’t follow the same laws of charity as by other paupers, but rather is all according to the affordability of the son and as to the ways of the world support one’s parents”; 8:166; Darkei Moshe 240 and Chasam Sofer Y.D. 229 in opinion of Tur; Amudei Arazim Mareches Nun Vav-4; Shevet Halevi 2:111-3; Teshuvos Vehanhagos 3:286; Encyclopedia Talmudit ibid footnote 363-366

[9] Rishon Letziyon 240

[10] Chasam Sofer Y.D. 229, brought and questioned in Shevilei Dovid 240, Shevet Halevi 2:111-3; 125; Teshuvos Vehanhagos 3:286.