think they might be able to just swap the frame if its a current frame. im an optical assistant - if they were free on the voucher they should be able to use a repair voucher to do it and it should be free. if you paid for them it will cost you the price of a new frame. if the frame is in stock they will do it for you there and then.
is your opticians normally open on a Sunday? (mine isn't). You could get the glasses replaced free of charge (I have never had to pay for repairs/replacements although I have always chosen the free frames for dd so far).
Thanks Guys didnt know opticians were open sundays but just googled and there is one close by that is, so thanks. will be taking him tomorrow. Should it matter if it is a different opticians from where we got the glasses?
yes - if he got the original frame from one opticians you may just be able to swap frames from the same one. id go back to where you got them. it might be quicker in the long run and cheaper too. unless its a chain like specsavers or vision express - in which case they use the same frames in each branch...