"Son left very upset after bloods taken"

I attended Forth Valley Royal Paeds dept recently with my son to have bloods taken. I tried to prepare him the best I could beforehand and told him that he would get special cream and he would be numb for it being done 

When we arrived a staff member taking the bloods asked if he knew why he was there (he is 5 years old) I explained that I had told him and that he would be numb (he had bloods taken last year and could remember the process)

I was told that he would not be numb but a cold spray would be used. He was very upset and the experience was quite traumatic for him. He said the cold spray did nothing and he could feel everything and was hysterical throughout

I just wish my appointment letter had a bit more information about the process of having bloods taken and what it would entail for a child. I just wrongly assumed he would be numb for it.  I would have bought numbing cream myself in preparation to save him from the distress it caused.