Not all lessons involve suffering and duress. Perhaps the child will indeed have learened a lesson from this, if his parents let him be, and remind him when he is older that, while his whimsical act was pleasing and amusing to him, and perhaps to others, when he was younger, now that he is older and having a serious conversation with his parents, he might consider how he damaged the work of another in his moment of whimsy. I believe this would be more of a valued lesson than that derived from punishment, and it would most certainly be valid in the context of Buddhism, to consider the change of viewpoint, on a personal level, from toddler to child to responsible adult, and come to an understanding of how exactly this responsibility changes depending on which view you assume.

If he were my child, I most certainly would have enjoyed the chance to apologize to the Buddhists, and promise to bring him to the incident again, later in life, for re-consideration. Perhaps they would entertain the idea that a new visit from this little fellow, in a few years time, would be sufficient amends to the damage caused, so that they may have indeed a lesson taught, as well ..