if he says he was hurt you absolutely have to find out what happened!
gut instinct above else, you know him best, you'd know if he's lying!
I'd go in today (so Friday) and ask "A" to tell you what happened on Monday as your son came home upset and you are naturally concerned. if she says nothing or denies anything talk to immediate boss of hers explaining it. they know him and someone must have seen or heard something. (don't leave it till Monday, she'll be all I don't remember and you'd be worried for entire weekend!)
if she did hurt him than that's quite serious, she should be removed without delay, no excuses!
I could do with a bit of advice my ds loves nursery now he goes 3 times a week but his key person had the day off monday so someone else looked after him (call her a). when i took him in yesterday the same lady tried taking him to play (his keyperson was at lunch) but he hid behind me clung to my leg and cried this is very unusual for him he usually goes in happily with any of them. in the end he went in with another lady and was fine. today he ds has told me he doesnt like a ifinally got out of him she hurt him on his back and told him to go away? ds is 3, he does tend to exagerate a bit at times and his speech is fantastic but im pretty sure thats what he said and obviously something happened with (a) monday for him to go in crying? What would you do? i dont want to go in accusing someonne i just dont really know what to say