The showrunner explained that he is excited about the next episode, PA reports.
"Episode four has the weeping angels and Alex Kingston returning," Moffat said. "I think it's one of the scariest ones we've ever done - my little boy says it's the scariest thing he's ever seen in Doctor Who.
"The first three [episodes] have been moderately scary. We're now going for proper scares in four and five, and in six actually, so some good spine-chilling stuff on its way."
Moffat added that he knows children watch the show to be scared, saying: "If you took a vote amongst the playgrounds of Britain they'd all be saying, 'Make it scary, you're meant to be behind that sofa!'."
Moffat also revealed that he is thrilled about the response to new Doctor Matt Smith.
He said: "I thought it'd take about four or five weeks to get to where we got after the first broadcast, but people just seem to have fallen in love with him instantly."
Doctor Who continues on Saturday at 6.20pm on BBC One.