The infected children were doubled by dwarf stunt people.
Tamra's line "circle circle dot dot, now you have a cootie shot" was included in the movie per the request of Leigh Whannell's wife, Corbett Tuck.
The second time that Elijah Wood plays a character who fights monsters in a school. The first time was in The Faculty (1998).
The photo featured in the beginning inside Clint's (Elijah Wood) bedroom is an actual picture of Wood as a kid.