Obviously all three of them should split the money three ways.
The dude playing baseball in the afternoon was the one who contributed the money for the cups and did a lot of lemon squeezing. The other guy sat at the stand all day even when there was no business but deserves to be paid for spending his time "minding the store". And Kid Brother, by sheer serendipity, found the slew of thirsty construction workers. He may not have been working, but that doesn't matter, being that without him they wouldn't have made a cent.
Each of them should get a buck.