You will need to set their Admissions status as Enrolled for this to occur. In Admin > Students > Admissions click on Bulk Update Admissions:
This takes you to a special Group Updater for your Admissions students. You select Admissions - Status from the Student Attribute dropdown, then choose 9 - Enrolled to apply to the students.
As long as they have a future entry date they will not appear in registers or reports as Current Students, but they will appear under Future Students. You will also find them in the Comms area under Future Students, and be able to print off student labels for them.