I mean, of course I believed at some point. When you’re young you believe your parents. I don’t have any specific memories about Tooth Fairy or Easter Bunny, but I remember my Santa moment very clearly.
My family had a tradition of a relative dressing up as Santa when we got together and coming to visit and passing out presents. I remember distinctly seeing my Uncle Bobby going upstairs, and wanting to talk to him about something (I don’t remember what). When I went to the stairs, his son Larry (who was a few years older than me) blocked me and was SUPER suspicious about getting me to not follow.
A short while later, Santa shows up, and thanks to my suspicion being up, I took a closer look than normal and realized it was Uncle Bobby. So that was my 1+1=2 moment. How old? Based on what house we were in it would have been between 7 and 10, but I can’t recall specifically.
My sister had a great moment where her belief was too strong for a mistake to break it. We were going on vacation over Xmas, and my parents wanted the santa gifts to be out by the tree when we returned so it would look like Santa arrived while we were gone. So we were lead outside while my father put them out.
Then, just before everything was shut and we were leaving, my sister decides she forgot something and runs inside before anyone can stop her. 10 seconds later, she bursts out of the house yelling “Santa knew we were going to be in Florida and came early!!!” Which I just think is adorable.
Per another part of the question – I do think we do kids a disservice when we lie to them about stuff like this. Sure, it seems harmless, but I think telling kids the truth whenever possible is the better policy. I particularly hate these ‘elf on a shelf’ type things where we try to teach kids that they’re being spied upon and stuff.