It won't be. I've run youth sports league websites on a variety of platforms. The platforms all suck in one way or another (most actually suck in many ways), but that's not the real problem. The real problem is that some portion of the user base/parents are hopelessly incompetent with technology and will consume your time with their problems or questions. Another segment will feign problems to try to get you to do their work for them, and at some point you will do it because it takes less time than spending time on a back-and-forth of questions and getting nowhere.

Just use email and/or text messaging.

throwawayboise is not wrong in any way, but if you want an answer anyway, I think it would be some kind of multi-platform massive automatic fusion. Good luck not accidentally creating, or automatically detecting, forwarding loops LOL.

So if you're one of the minority of parents smart enough to import a calendar into their google (or other) calendar, they can get the game schedule there, but the less competent (to put it nicely) can continue to get a stream of emails or even plain old text messages of upcoming games. Or they could join a FB group or a different platform.

Or there's people out there whom could never handle installing or using slack, but if you could spam them text messages maybe they could still participate, or even participate fully.

Nobody wants to work in IT, especially not for free.

We went thru an internet era, then a social era, then the era of notifications, and I have a gut feeling the next era is going to be something like smooth automatic operations across semi-hostile deeply silo'd platforms, but it'll have a cooler name. FB wants to replace the internet with FB, but literally nobody else wants that, repeat for all platforms, meanwhile you get 5 users together somehow you'll get 6 preferred platforms, the next era will be anti-vendor lockin. People old as me will remember when Ma Bell provided both your phone service and your physical phone and times were better post-divestment and that's probably how we're going to look at the past once we're beyond the era of the social media silo. Rather than "the world is viewed thru my website for my profit" the future will be something like "the world is viewed thru my REST API or maybe many other API providers" And where the profit comes from is mysterious. Likely the gateway tech will be workable microtransactions. Such that every time Sally Softball Mom checks the team schedule she will get billed and you will get a hundredth of a cent, which isn't going to scare away 10M daily users but would be a nice side gig for you personally. Assuming you get 10M DAU of course.