; (D) by inserting for a taxable year beginning after December 31, 2017, and before January 1, 2026, after under this section in paragraph (2), as so redesignated; and (E) by striking for taxable years 2018 through 2025 in the heading. (b) Increase in credit for young children Subsection (a) of section 24 , as amended by subsection (a)(1), is amended by striking $2,000 and inserting $2,000 ($3,000 in the case of a qualifying child who has not attained age 6) . (c) Adjustment for inflation Section 24 is amended by redesignating subsection (h), as amended by subsection (a)(3) of this section, as subsection (i) and by inserting after subsection (g) the following new subsection: (h) Adjustment for inflation (1) In general In the case of any taxable year beginning after 2019, each of the dollar amounts in subsection (a) shall be increased by an amount equal to— (A) such dollar amount, multiplied by (B) the cost-of-living adjustment determined under section 1(f)(3) for the calendar year in which the taxable year begins, determined by substituting calendar year 2018 for calendar year 2016 in subparagraph (A)(ii) thereof. (2) Rounding If any amount as adjusted under paragraph (1) is not a multiple of $50, such amount shall be rounded to the next lowest multiple of $50. . (d) Modification of qualifying child definition Paragraph (1) of section 24(c) is amended by inserting , determined without regard to paragraph (1)(D) thereof after section 152(c) . (e) Treatment as fully refundable (1) Credit moved to subpart relating to refundable credits (A) In general The Internal Revenue Code of 1986 is amended— (i) by redesignating section 24, as amended by this section, as section 36C