A preliminary hearing began Monday near Toronto for four youths accused of belonging to a group that was allegedly planning to bomb targets in Ontario.

The four, all under 18, were arrested last summer with 14 adults. The young defendants face charges of belonging to a terrorist organization and attending a terror training camp.

The case has received attention from around the world, but the preliminary hearing is subject to a publication ban and the evidence cannot be reported.

Michael Block, the lawyer for one of the four youths, said the hearing in Brampton will sift through information that could later be presented as evidence before a judge and jury in Ontario Superior Court.

Block said the hearing was expected to last four weeks, but more time may be needed because defence lawyers have had to wade through a vast amount of data gleaned from three computer hard drives.

"My hunch is that period of time might be inadequate … based on tens of thousands of pages of disclosure and quite a bit of videotape," Block told CBC Newsworld on Monday.

Reports have put the number of Crown documents at two million pages.

"It does have a bit of needle-in-the-haystack kind of quality, especially, I can say, in relation to my client, whose alleged role in this is somewhat minor.

"But the Crown has provided this disclosure by way of a hard drive, so that you can do an electronic search, a key words search, a search based on your client's name.

"It seems to be fairly well-organized … an ingenious way of providing the disclosure and the only way that would make sense in the present context."

Three of the four young suspects are out on bail, while the fourth remains in custody.

The 14 adults will be tried separately and are expected to appear in court next week to set a date for their preliminary hearing.