Washington (CNN) Donald Trump said Monday that his children, Eric and Ivanka, "feel very, very guilty" they will be unable to vote for him in New York's primary next week because they missed the state's voter registration deadline.

"They had a long time to register and they were unaware of the rules so they feel very, very guilty, they feel very guilty, but it's fine, I understand, that," the real estate mogul said on Fox News' "Fox and Friends." "I think they have to register a year in advance so Eric and Ivanka I guess won't be voting."

Eric and Ivanka needed to have changed their registration to Republican by October 9, 2015 in order to vote in the state's closed primary. Yahoo News reported last week that the two Trump children were not registered with any party.

The two called New York's registration process "one of the most onerous" in a statement and argued the deadline for changing their party registration was October 2015. T he New York State Board of Elections states anyone must register before March 25, but in order to switch parties voters had to file before October 9, 2015.

"Each state differs greatly in terms of the rules and requirements--most allowing you to change your status on or close to the date of voting, if even required. Eric and I are fully supportive of our father and look forward to casting our vote for him in November," Eric and Ivanka Trump said in a statement.

Trump also said that despite calls to put her on his ticket, Ivanka Trump will not be his running mate.

"I wouldn't be doing that, although a lot of people would like to see that. A lot of people would like that choice but it wont happen, that I will tell you, it won't happen," Trump said, when asked if he would select his daughter as his running mate.

The real estate mogul jokingly floated her name as a possible running mate last year, before quickly saying he was kidding.

Trump also used the interview to slam primary rival Ted Cruz's campaign as well as the Colorado delegation allocation process, which over the weekend awarded Cruz all of its 13 final pledged delegates

Trump called the process "a crooked deal," and said his Colorado supporters are "going absolutely crazy because they weren't given a vote."

"Well that really shouldn't be the way it is. This was changed in the summer to help a guy like Cruz and it's not right."