Hi MiriamC
I would contact the assessment provider now (number will be on the letter) and tell them. You need to warn them you wish to bring a baby into that environment. There will be H&S issues they might need to consider.
The assessor will want to hear from your son. It really does depend on what the assessor is like whether at any time you will be allowed to speak for him. You need to play this by ear. Some are very good and make it clear from the beginning what you are allowed to do or not do. Some are less so and can be hostile about a relative speaking. If you try and interrupt without prior invitation, it can cause problems and we have known in extreme cases of the assessor stopping the assessment.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
