I don't think it would be as scary if they weren't little kids. I mean, it would be fucking scary if you opened the door and there was a bloke standing there dressed like that, but scary in a different way. It takes little kids to be Sapphire and Steel creepy.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'