I assume this mean's Stephens and Ward-Prowse will have a first team role this season which is brilliant although I'm surprised that as they are included that Luke Shaw didn't get the nod too but on the other hand I think he may be a year younger than the pair and may not be quite ready.
Don't quote me on this if I'm wrong but I'm sure the squad numbers that have been released isn't a definitive list of those currently at the club that can be expect to be in and around the first team this season.
Obviously as new players are signed they will be given new numbers so I'm sure there's nothing stopping some of the younger players like Shaw and Hoskins being given a number if they start to impress in the U21's.