"My kids were embarrassed by it, and if I had to do it again I wouldn't."
Rubio had previously shied away from direct confrontation with Trump, but he burst out of the gate in the last debate before Super Tuesday by emptying the opposition research file against Trump.
The next morning, he bashed the billionaire as a "con artist" on television and days later poked fun at Trump's hands for being small.
"You know what they say about men with small hands?" Rubio said at a Feb. 26 rally. "You can’t trust them.”
Despite the more aggressive tack, the Florida senator hasn't gained traction in the GOP nomination fight, falling hundreds of delegates behind Trump and Ted CruzTed CruzCruz: Trump hasn't apologized for personal insults Cruz says he forgives Trump for attacks on family Why Cruz flipped on Trump MORE
. His campaign has pinned all of its hopes on next week's Florida primary.
Rubio also told MSNBC that he wouldn't be anyone's running mate -- including Trump's -- if asked. "I'm running for president."