And fans who are hoping to see the boys play themselves - a bit like in the S Club movie - could be disappointed.
"It's not going to be in 'Busted World'," said James.
"It's going to be like an English American pie with us in it, " added Matt.
The boys also said they'd like to see Edward Norton and Macaulay Culkin star in the flick with them.
"[Edward Norton's] a legend!" said Charlie.
But don't rush off to reserve your cinema tickets just yet.
The boys have only just started writing so it won't be out for at least two years!