I was taught about the Real Presence right from the start.
I can only remember doubting it once, when I was a child. It’s actually sort of silly. I absolutely loved a kids movie with a fairy/angel/grandmother character that used magic, and every time she did small bells could be heard in the soundtrack. So I associated the sound of small, unseen bells with magic (you can probably see where this is going). Due to my small size and where my family chose to sit at Mass, I couldn’t see the altar server ringing the bells. But I never questioned where the sound was coming from - I thought it was the sound of God’s magic changing the bread and wine into the Body and Blood! I even went as far as to think that unbelievers were very silly for doubting when I could so clearly hear God’s power at work.
Then one day we sat somewhere different, and I saw the little bells and the altar boy ringing them. I realized I might be expected to believe without proof.
Me: Mom - mom, that boy is ringing bells.
Mom: He does that every Mass. Hush now, this is an important part.
Me: …But Mom, is that REALLY Jesus?
Mom, looking shocked: Yes, of course!
And I never doubted again.