I imagine that aliens would get over the concept of baby teeth fairly quickly. Sure, there are a few cases of aliens who have been left to babysit friend’s children freaking out when the kid comes up to them holding out one of their teeth and excitedly talking about the tooth fairy— but I’m sure they’d get over it.
Lots of species have weird aging things like skin shedding or growing spines. And the parents have come up with a story about a fairy to lessen the horror. Okay.
But y'know what I think would freak them out? The lengths some kids go to to get that sweet tooth fairy money.
Little kids asking for crunchy apples because they want to lose a tooth on them. Adults talking about when they were a little kid and tried the old “use string to tie the tooth to a door knob and then slam the door” trick. Or just straight up pulling the kids’ teeth out themselves.
Aliens are reminded how we got the nickname ‘space orcs’ as we rip the teeth out of our mouths for cash.