@keekee53
...When you make a cake, put the candles on it. Place it in the fridge with the candles on and the sims will not be able to grab a slice of cake.
Thank you for pointing out that trick, that's exactly what I do, add candles! However, I don't put it in the refrigerator because it can still spoil in there whereas in the household inventory, it'll last forever.
If you're going to use it within a couple weeks or so, the fridge works fine to temporarily store a cake topped with candles so it doesn't get eaten. Although I have read threads where somehow Sims are still able to eat cakes with candles on them in the fridge. *shrugs*
For me though, birthday cakes are rarely ever eaten after the candles are blown out. I have the newly aged Sim add more candles and it goes back in the household inventory to sit until the next Sim's birthday, which can be several seasons away.
Thanks again though for posting the trick for those who didn't already know, very helpful! :)