I think they probably meant documents needed for the court bundle (which you already have) when it's needed.
If you're self repping for this upcoming hearing, then sending a good position statement in advance can do a lot of the speaking for you. You need to decide what kind of outcome you want and whether you think a section 7 report would be of benefit or not. And argue the points in your position statement. A position statement is quite straightforward - it's basically a "note" to the Judge before a hearing updating "the position" ie anything that's happened since the previous hearing, anything you want to say at this stage and what you would like the court to do.
If your ex has a solicitor on the day they might dominate the proceedings somewhat, so be prepared for that. If they push for a section 7 then just accept it - it could work out for the best even if it takes longer. However it means Cafcass will be involved again and they might recommend both kids live with one parent and spend time with the other (and it's usually the Mum).
The other thing is whether you think a fact find would be helpful. If you have evidence that she's dangerous to the kids eg. It is a tricky situation as she's been allowed to take your son on holiday but only has supervised time with your daughter.
Start putting something together for a position statement - I'm happy to have a look over it.