Ask for a copy of all reports, tests, analysis results, clinical documentation, scans etc. For a second opinion or for participation in studies and so on, these will be very useful, and could help your child avoid tests which have already been carried out. It will also be useful at times when your child is not in hospital and has to go to the emergency room.
In most countries, you will have the right to this information by law. While unfortunately in some hospitals they do not obey this law, remember to exercise your rights and those of your child.
Remember that they cannot give them to you immediately, so the sooner you ask for them the better.
Our recommendation is that when you ask for them, specify which documents you want, and add that you also want any other documentation which might exist, always citing the relevant law in your country.
It might also be useful to keep a diary of the illness, its progression, medical assessments, etc.
This can help to record new symptoms to show to doctors. On occasions, the reality can get distorted in the process of a parent detecting and describing a symptom, and a doctor evaluating it.