you know , my daughter felt the same as you when i told her ...
At age 7 I thought it best to tell her myself before someone at school told her... and she was horrified... she took a step back looked at me wide eyed,,, and said accusingly '' You Lied''... why did you lie to me''...?
She'd been going through a period of telling me little fibs she'd picked up at school age around 6.. and I had told her over and over how unacceptable it was to not tell the truth.. so when i confessed about no Santa when she was 7 .. she felt utterly betrayed by me.. and it breaks my heart to this day.... because even now she's 49, if I bring it up, she'll still say.. why did you tell a lie in the first place !