He probably doesn't actually understand that it's wrong to mistreat other people's possessions in this way, nor that it's 'wrong' because it's potentially dangerous, but he should be learning that mother doesn't want him to do it. How she achieves that (or not, as the case may be) is an emotive matter.
When mine were that age, a slapped hand or a sharp word when they did things I didn't want them to were enough to stop them. Eventually they learnt that, for example, climbing onto coffee tables wasn't such a good idea and the best way not to be punished is not to do it. The method has been good enough for generations of human and animal parents with no ill effect (that's as long as it's used sensibly - I'm not condoning physical abuse here).
But of course today you aren't supposed to smack children, even lightly, and you aren't supposed to snap, swear or shout at them. Now, I used to know a nursery school teacher who never, in all the time I knew her, raised her voice at or showed anger towards her charges, yet they always knew when they'd done something wrong and when she wasn't pleased with them. She just had that knack. Not everyone can be like that, though, no matter how hard they try. So their children just get away with everything because they no other legal way of disciplining them.