Just saying, if you ignore the lightning warning siren and keep the kid on the soccer field anyway, or ignore the shark alerts and leave the kid in the water off the cape thrashing about, you greatly increase the risk. If you ignore the COVID rate and take the kid into poorly ventilated spaces with lots of random people from all over, you increase their risk too.
You pick your own items, but someone unable to vaccinate a 4 year old choosing not to increase their risk for a vacation doesn’t sound that strange. Even rare, if you happen to hit that one, you’ll feel like crap forever.
We barely had seatbelts in the back seat, much less car seats. Millions of trips a day result in nothing, yet we buckle them in, just in case.
Lots of people will take that chance, most will fine. But for one that’s not, it may change their life forever in a bad way. Not like getting a splinter that’s gone and forgotten a day later.