What did Kevin think was going to happen?
He stole his Dad's money and credit cards, what exactly was his end game? Did he plan on just living by himself in the Plaza for the rest of his life, or did he eventually plan on reconciling with his family? Because if he planned on the latter he had to realize that he was going to be in a sh!t load of trouble for stealing his Dad's money.
Now usually I would buy the excuse that Kevin was just a kid and didn't have the ability to foresee the consequences of his actions but it was clearly established that he was really smart and considering the fact that he was able to fool the hotel staff into giving him a room I am not going to buy that excuse.