Can citizens who are on low income file for their children?

Although not completely clear from your question, I presume that you are a U.S. citizen, your income is relatively low, and you are interested in petitioning for your children to get immigration benefits. If my understanding is correct, then be aware that a citizen's income is merely one detail involved in determining immigration eligibility, and if (1) eligibility requirements otherwise are satisfied, and (2) the petitioning U.S. citizen has insufficient documentable income to meet the Affidavit of Support requirements, then it may become necessary to have a joint sponsor in the application process. Generally, a joint sponsor may be any U.S. citizen or Permanent Resident who has sufficient documentable income and who is willing to assume the responsibilities contemplated in the Affidavit of Support. It would be wise for you to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options, and strategies to attain your goals, and who then could offer legal representation in the often complex application process.

Yes, but they will need a joint sponsor.