The deadline for new voters to register to vote in New York's closed primary was March 25, and the deadline to change party affiliation was back in October.
"Eric and Ivanka, I guess, won't be voting," Trump said.
See more images of the Trump family:
Members of the Trump family
2 of Trump's kids missed NY registration deadline, can't vote for dad
NEW YORK, NY - MARCH 26: Ivanka Trump and Jared Kushner are seen on March 26, 2016 in New York City. (Photo by Tal Rubin/GC Images)
BRIARCLIFF MANOR, NY - SEPTEMBER 21: Jared Kushner and Ivanka Trump attends the 9th Annual Eric Trump Foundation golf invitational at Trump National Golf Club Westchester on September 21, 2015 in Briarcliff Manor City. (Photo by Bobby Bank/WireImage)
BRIARCLIFF MANOR, NY - SEPTEMBER 21: (L-R) Vanessa Trump, Donald Trump Jr., Ivana Trump, Eric Trump, Lara Trump, Ivanka Trump and Jared Kushner attend the 9th Annual Eric Trump Foundation Golf Invitational Auction & Dinner at Trump National Golf Club Westchester on September 21, 2015 in Briarcliff Manor, New York. (Photo by Grant Lamos IV/Getty Images)
NEW YORK, NY - MAY 04: Jared Kushner and Ivanka Trump attend the 'China: Through The Looking Glass' Costume Institute Benefit Gala at the Metropolitan Museum of Art on May 4, 2015 in New York City. (Photo by Axelle/Bauer-Griffin/FilmMagic)
NEW YORK, NY - JUNE 16: (L-R) Eric Trump, Lara Yunaska Trump, Donald Trump, Barron Trump, Melania Trump, Vanessa Haydon Trump, Kai Madison Trump, Donald Trump Jr., Donald John Trump III, Ivanka Trump, Jared Kushner, and Tiffany Trump pose for photos on stage after Donald Trump announced his candidacy for the U.S. presidency at Trump Tower on June 16, 2015 in New York City. Trump is the 12th Republican who has announced running for the White House. (Photo by Christopher Gregory/Getty Images)
NEW YORK, NY - JUNE 07: Jared Kushner (L) and Ivanka Trump attend the American Theatre Wing's 69th Annual Tony Awards at Radio City Music Hall on June 7, 2015 in New York City. (Photo by Mark Sagliocco/Getty Images)
BEDMINSTER, NJ - OCTOBER, 25: In this handout image provided by Ivanka Trump and Jared Kushner, Ivanka Trump (R) and Jared Kushner (L) attend their wedding at Trump National Golf Club on October 25, 2009 in Bedminster, New Jersey. (Photo Brian Marcus/Fred Marcus Photography via Getty Images)
Donald Trump, president and chief executive of Trump Organization Inc. and 2016 Republican presidential candidate, center, speaks as his sons Donald Trump Jr., left, and Eric Trump, right, listen during a caucus night rally in Las Vegas, Nevada, U.S., on Tuesday, Feb. 23, 2016. Trump's dominating victory in the Nevada caucuses pushes him further out ahead of his nearest competitors for the Republican presidential nomination, giving his unorthodox candidacy a major boost heading into Super Tuesday contests next week. Photographer: David Paul Morris/Bloomberg via Getty Images
20/20 - Donald Trump and his family - including wife Melania Trump and his children - sit down for an interview with ABC News' Barbara Walters in a special edition of 20/20 airing Friday, Nov. 20 (10-11pm, ET) on the ABC Television Network. (Photo by Lorenzo Bevilaqua/ABC via Getty Images) DONALD TRUMP, JR., IVANKA TRUMP, ERIC TRUMP, TIFFANY TRUMP, BARBARA WALTERS
LONDON, ENGLAND - JULY 28: Marla Maples (L) and Tiffany Trump have dinner at Sumosan on July 28, 2014 in London, England. (Photo by David M. Benett/Getty Images)
BRIARCLIFF MANOR, NY - SEPTEMBER 15: (EDITORS NOTE: Retransmission of #455504994 with alternate crop.) (L-R) Donald Trump, Ivana Trump, Eric Trump and Lara Yunaska attend The Eric Trump 8th Annual Golf Tournament at Trump National Golf Club Westchester on September 15, 2014 in Briarcliff Manor, New York. (Photo by Dave Kotinsky/Getty Images)
NEW YORK, NY - APRIL 18: Donald Trump, Eric Trump and Lara Yunaska attend the New York Observer's 2013 Young Philanthropy event at PH-D Rooftop Lounge at Dream Downtown on April 18, 2013 in New York City. (Photo by Laura Cavanaugh/Getty Images)
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Trump's campaign has been plagued in recent weeks by poor organization in local and state-level Republican conventions, where delegates to the Republican National Convention are selected.
In several states over the weekend, the delegates chosen at the party gatherings were Ted Cruz's loyalists, who could support the Texas senator on the convention floor if the nomination race goes to a second ballot.