Neil Patrick Harris shows off pictures of twins Gideon and Harper on 'Letterman'

"How I Met Your Mother" star and last year/this year's Tony Awards host Neil Patrick Harris was on "The Late Show with David Letterman" Thursday night (June 9), but the talk first turned to babies. NPH and his partner David Burtka have twin babies, Gideon and Harper, who were born back in October 2010. Letterman asks where they got those names and NPH goes ... a different way with his answer.

"I'm Neil, N-E-I-L and there's also another spelling of Neal, N-E-A-L, and that drives me batty because I get mail that's to 'Ne-AL' not 'Ne-IL' and I said if I ever have kids, I want to make sure that their names are unique enough that they're unique, but that they're easy enough to spell. They have simple spellings."

So it's really a postage mixup that brought about the names, cracks Letterman.

NPH then reveals that they've been taking themed pictures of the twins and shows off the below photos.

"We do one a month, we're doing a calendar, so that that when they're older, we can humiliate them."

Um, we would totally buy that calendar.