absolutely do nothing. let him make his own choices
things like that can cause hangups in later life - especially if its a favourite toy... it can show in odd ways like becoming a hoarder, stealing, being extremely private, being posessive etc
may sound over the top - but can give a child a sense of loss of belongings, of losing control over possesions, of feeling violated etc etc ...
they dont understand the emotions, but the feelings can linger and manifest in later life...
my parents used to take our stuff and sell it in one of their shops... id walk in the shop and see my stuff on the shelves and it infuriated me - the cheek of it! ...
most of the time we didnt even notice, and they took things we didnt use anymore so they thought we wouldnt care... and mostly we didnt...but now and again theyd get it wrong and take something special and thered be a row...
never forgot that feeling - especially since there would be no apology just shouting and the assertion that they paid for it in the first place so they were entitled to take it! ...