There are a few pieces of missing information, but this is my 2 cents worth. As described by definition this is a single story. The deck is a second level. A constructed playhouse would be an accessory structure in accordance with the IRC. Then the 108.2 exception would not require a permit, but compliance with the code, such as R302.1 exception 3, R403.1 exception 1.
102.3 is a copy of the Amusement Device Regulation section 13VAC5-31-30, “a device or structure open to the public” that is exempt from the code.
