No, I am sorry.
Their lost and found policies are not law.
Come what may, they didn't have any duty at all to take any care over this pursue. Ultimately they weren't responsible for it.
The fact that they did is more than the law requires.
There is obviously a case against the person who took it but you have to identify him.
The only possible claim against McDonalds is to argue that they became a bailee of the pursue but, if I am wholly honest, that is fairly weak.
The only purpose in bringing a claim at all is in the hope that McDonalds will not consider it worth contesting and settle which might happen.
You should be aware though that if they do refuse you would lose at court.
I'm very sorry
Can I clarify anything for you?