There are a lot of anachronisms in the two first Monkey Island: The T-shirts, the grog machines, the costume shop, the maintenance tunnels and room, the underground ticket (E-ticket)...
Booty Island (whith the costume shop) and Big Whoop entrance can be superposed:
I think that if you only play SoMI and MI2, the
child's mind is the most likely theory.
In an
interview, Ron Gilbert said that he would love to make an other MI and share his secret with the world. I would love that too

...
In my dreams, Telltales would announce the development of MI3 Prime - The Revelation, the Ron Gilbert non cannon version. I wouldn't mind if it's an old SCUMM based point and click adventure game if it can lower the development costs (actually, I would even prefer

).
It could start right after the end scene of MI2, Guybrush suddenly runs away, parents and Chucky stands puzzled, finally Chucky decides to go after him. Guybrush enters an attraction with his E-ticket (Chucky doesn't have one). Then, progressive transition back to the dream realm: For example Guybrush climbs a ladder and emerge from the hole where Elaine is waiting, but the screen is "half dream, half real". Guybrush doubts. Elaine manage to convince him that he was cursed by LeChuck, take his hands, Guybrush closes his eyes, and when he opens them again, there is no confusion => Back to a pirate adventure. During the game, more and more anachronisms, some of them makes Guybrush very uncomfortable. In the end, the world become very unstable, sometimes, Guybrush go back in the theme park... In reality, Elaine could be a girlfriend, or a even an action figure/doll (shock! in porc
elain! shock! shock! That could explain something, if porcelain reminds him that he is in a dream...) that Guybrush forgot in the end of MI2...
Obviously, this can't be what Ron Gilbert had in mind, his secret is still secret, unfortunately...