OK OP, so I think your argument for not being sacked/disciplined is this:
- Your safety system relies on you being provided with a booklet detailing students and their allergies, from someone else within the school. You had requested this earlier this term but been told it "was not ready". (Do you have an email detailing this request? If so, keep it - it might be useful. If not, try to remember when you asked and who you asked, and make a note of this if you haven't already).
- In the absence of the booklet, WHICH YOU HAD REQUESTED, you did the best you could by pointing out the child to your staff member and telling them not to give the child food containing certain allergens. Your staff member, however, forgot this.
I agree that you cannot monitor every single thing your staff members do - you rely on them following instructions. Expecting them to do it from memory is a big ask, but given that you had requested the booklet. (Just once? Or more than once?) and been told it wasn't ready, you did the best you could. You are not allowed to create and display a poster showing photos of the children and their allergens, so without the booklet you have to rely on memory.
Based on all that, it's not your fault. I think your staff member could be disciplined for this possibly, but could reasonably argue that being asked to do this from memory is too challenging - if a child changes their hairstyle or whatever it can be difficult to recognise them.....
The booklet is a good solution and has I assume been effective in safeguarding children before. So I would think that, if anybody is to blame, it's the person who has not produced the booklet. Either the person who makes it, if they just hadn't bothered getting it done on time, or possibly their line manager, if they KNEW it wasn't ready and were telling them to prioritise other actions.....
Given the different opinions on this thread though, this is clearly not obvious to everyone (though I have worked in management and safeguarding in schools and I have to say it DOES seem clear to me. But interpretations can vary). I would therefore strongly advise you to inform your union if you have one, to get everything written down ASAP, and not to go to meetings about this alone, especially if you lack confidence in being able to defend yourself clearly, etc.
And again, I think it's a point of vital importance that you asked for the booklet and were not given it. So if you can prove that with an email, or even if a colleague witnessed you asking, that is even better.