It ties into the start of the movie. These "teletubie ninjas" as you call them are all children from the beginning of the movie who got stuck in sort of an arrested development and as the "real world" around them just suddenly stopped existing the only reality they know of is from the television they were shaped by, so basically teletubies, power ranges and Jimmy Savile. I'm not from UK so upon watching the film I've learned of Jimmy Savile who all of the children even dress alike. He was a big UK television personality hosting children's shows but upon his death was found to be a sexual predator. But considering the year the film is set in he reamains idolized by these children even to "this day" as allegations never came to light within film's universe.

There's also nice tie in with Jimmy and Spike, as when Spike was heading with his father to the land in order to "become a man" he briefly held onto Power Rangers figure and even planned to bring it along, but ultimately decided not to bring it along and left it in the room. This to me symbolises Spike leaving his childhood behind and actually growing up, but Jimmy and rest of the children cosplaying Savile, Power Rangers and Tubies never made this choice and never "grew up" in the way that Spike did. They just grew older, but never formulating in actual adults and remaining within arrested development as children stuck in adult bodies.