Yes they probably will stop you from drinking

Disney is crazy anal about underage drinking. They card EVERYONE.
I was about a week from my 21st bday and went to Pleasure Island with some girlfriends (also under 21). We drank a bit before we went, but were not drinking at PI. I was SOOOOO thirsty, so I asked for a glass of ice water from the bar. Apparently the bartender gave me the wrong cup because within 2 minutes I had all kinds of Disney security all over me asking to see my ID. When I tried to explain that it was only ice, they walked me over to the bartender I used, lectured him, and poured my ice water into a paper cup!!