"Certainly, we have children and marriage is an appropriate thing to do [as] a part of their well being, so I'm sure it will be inevitable—and awesome!" Harris told E! News' Marc Malkin at the "Michael Jackson ONE" show in Las Vegas, which was also attended by Jackson family members over the weekend.
Harris and Burtka welcomed twins Harper and Gideon via surrogate in 2010.
Harris also used the word "inevitable" to describe last week's landmark Supreme Court rulings on the Defense of Marriage Act and Proposition 8.
"I'm not one who jumps around and cheers and screams because I thought that was inevitable and was going to happen," he said of the justices' decisions in favor of gay marriage.
"It's logical. If you look at public opinion polls, everyone, the majority of people, are very for people that fall in love with each other being able to own that," he added.
But Harris stilled had his "fingers crossed" last Wednesday, and tweeted his excitement when the court struck down DOMA.
Fingers crossed… #equality— Neil Patrick Harris (@ActuallyNPH) June 26, 2013
DOMA-it-just-lost-O Mr. Roboto! So, so happy for Edie, et al.— Neil Patrick Harris (@ActuallyNPH) June 26, 2013
And Prop 8 was dismissed?!? Huzzah! Christmas comes six months early this year! (Less one day…)— Neil Patrick Harris (@ActuallyNPH) June 26, 2013