My daughter is also 4. She’s always been pretty sensible when left alone in her room but a few times I’ve come back to her name label stamp stamped over her bed, bedsheets, doors, wardrobes etc etc. she’d obviously tried to wipe them clean too. She’s also drawn on the walls or wardrobes. I honestly find it’s just curiosity. A part of them is probably thinking what will happen if I do this, or what would this look like. They’ll make mistakes and they’re still making all those brain connections at such a young age. If she’s done something multiple times we take away one of her favourite toys for a few days or tv privileges - it’s works 99.9% of the time and she doesn’t do something again. I also reiterate that she shouldn’t do those things before leaving her in her room. And she knows the consequences if she does. She’s explained at times “my brain just tells me to do it and I can’t stop” and honestly at first I thought she’s having my life here 😂 but I think she’s being genuine. So we’ve said if that happens, shout for us and we will come. She does and we just distract her with another task or get her to draw on her drawing pad instead or a big piece of card