I will totally disagree! It is 'not' normal behavior for a nearly 6 year old to smash a birthday cake! Curious child has nothing to do with it - I've had three curious children that age and they well knew how to behave, also knew there were 'consequences' for not doing so.
Sounds like a jealous kid being bratty, but she might have thought the fondant was more solid than it was and wouldn't be messed up easily. It would look pretty solid to a kid.
The OP clarified above that she did not smash a birthday cake, she just damaged the Olaf. The OP used the word mangled, in regard to the Olaf, but that doen't mean that the child intentionally crushed it, as everyone seems to be assuming. Sure, the child did something wrong by touching something that she was not supposed to- but she is 5 and they occasionally do touch things after being told not to- and it has not been stated if it was explained to her why she should not touch it- i.e. because it was made basically of sugar and was very fragile and could easily break. OP can correct me if I'm wrong, but I'm guessing OP is the birthday kid's mother who probably spent a lot of money on that fondant cake, and was very upset by Olaf being damaged. As stated by the other poster, a fondant Olaf looks solid. It also can look like it is an actual toy- again the OP stated she was told not to touch, but does not state whether it was explained to the child that it was actually made out of fragile sugar, and was not a toy. If you have ever dealt with fondant, you know fondant figures can sometimes crush, break, or even shatter at the slightest touch (or if not stable on the cake, can fall over and smash), even more so if the figure was actually made out of solid fondant, and no gumpaste was used- fondant can be notoriously unstable if it is not just right, which is why for figures, gumpaste is often entirely used for them or as a mixture with fondant. Also, if the fondant is not set, or if the cake with the figure on it was put in the refrigerator, then the fondant can become soft and mushy and and can smoosh when barely touched. Everyone seems to be assuming that this child picked up Olaf and intentionally crushed him. It is also possible with him being fondant, that she just touched him with one or two fingers out of curiousity, and he fell apart, or mushed. Or, she could have barely touched him with a finger and he fell over, and then she tried to fix it, by picking him up and putting him back right and she mushed him when she picked him up to fix it. That is typical 5 year old behavior. DD had a Frozen birthday party when she turned 8 last year and had a cake with Frozen figures on it- and although I told the kids not to touch the cake, I turned around and 2 of her guests were touching the figures on top of the cake. They didn't pick them up and didn't mean any harm by it, but if the figures had been fondant instead of plastic, they would have been done for. Those kids were not being cruel. They just loved Frozen, were full of party energy, and were curious about, or wanted to touch the figures even though they had been told to leave the cake alone. They were doing something they were not supposed to do, but they did not intend harm, and would have been very upset if they had hurt the figures or the cake. Totally normal hyped up kid party behavior-still wrong- but kids aren't perfect. Now, if she intentionally picked it up and crushed it in front of the birthday child out of anger or spite and was not remotely sorry afterwards, that is an entirely different situation. That is pretty bratty behavior.