We just ran a parents’ sports day at our PTA summer fair. Originally, this was because there are no Mums' or Dads' races at the kids’ sports day (probably for good reason!), and because it’s a great opportunity to raise money for the PTA.
However, it also brought more people along to the summer fair, got them there earlier in the day (and ensured they were thirsty). In a wider context, the event was great for raising awareness of activity through the school, and creating a lot of fun for the kids.