URGENT HELP VISA APPLICATION

[shilewa]

Hello everyone pls I'm trying to fill my sons visa form as a tier 2 dependent. there's a part confusing me. The section for main applicant the part that says are you accompanying the main applicant or coming at a later date.... Then at the side it says number of travel document main applicant is travelling to the UK with.
Will this be just the passport number or stating whether accompanying or not.
An urgent reply will be appreciated.
Thanks.