As nearly as I can tell, over half the money goes to support the Shriner’s activities, while the Shriner hospitals get about 2% of their operating budgets from Shriner fundraising. I don’t think the evidence is there, at any rate, that the various circus fundraisers do much good:
nytimes.com/2007/03/19/us/19shrine.html?pagewanted=5&_r=1&ref=shriners.
Also, the Shriners typically contract out their circus contracts, which means you have no idea whether the animal handlers will either be reputable with regards to their handling of the animals, let alone competent in providing entertainment. To my mind, this is no small thing, but this is just me.
As far as the Shriners’ connections with Freemasonry, you cannot be of the world, but you can’t leave the world, either. The Shriners all have to believe in “a Supreme Being”, but according to them, that is as far into religion as they get. The Church has found their philosophies in error, but that means only that their philosophy is not compatibale with Catholicism. That hardly puts them in the minority among people who characterize themselves as deists. After all, it wouldn’t be a sin to go to a show put on by the drama club at a Jewish high school or to a Middle Eastern cultural fair put on by a mosque. Nobody thinks that makes you a supporter of Judaism or Islam.
Going to a Shriner Circus is unlikely to encourage your son to become a Shriner, nor is it going to be taken by society at large as endorsement of Freemasonry. Being on the internet probably puts you into far shader associations than the Freemasons. You will probably be giving money to a bunch of guys whose organization is admittedly secretive about how they spend their time and money and who vastly oversell the degree to which their activities benefit children. That’s not unusual in the world of entertainment or fundraising, but it is something to think about.
Honestly, I would be most concerned about giving your son a traumatic and lifelong dislike of clowns.
