Yay and Congratulations of meeting such a fun milestone for the family!
My family never utilized rider swap as DH was more than happy to sit out some attractions, and I the ones he didn’t want to miss.
So we were just as anxious for then DS8 to be in the world for the first time that he could remember, and be tall enough to ride anything he wanted. In fact, his very first “upside down” coaster was RnRC. Which he then insisted on riding 3 more times in a row! After that, we were able to show that everything else was “tame” compared to his now favorite attraction. Other than Hulk at Universal, he willingly went on everything else with no issues. In fact, our trip next month will be his first on Hulk (now DS13) and he’s SUPER excited.
As a previous CM I had quite a few kids (and some adults) bail at loading. Back then we just did the last minute rider swap. Honestly, it depends on the discretion of the CMs. If it’s an attraction like Teacups or Carousel they may let the youngest sit out at the Exit gate and wait for the family to ride. If it’s one of the Mountains, they may force someone older off to wait with them.
I will say ToT…he hated. But I think that was more to do with the drops and his motion sickness more than anything else. And BTW I hate it too, I only do it for the theming.
I don’t personally recommend what we did with RnRC. I think we lucked out because he couldn’t see the track even after we rode so there wasn’t any long term “I’m putting you both in an old person’s home the minute you turn 65” going on.