@froggylady4020,
It's a hard decision either way.
Our last dog was very old (15) and ill and my daughter also grew up with him, he was her "brother".
At first I didn't know what to do either, then I decided that I didn't want her
burden with it and called a mobile veterinarian to the house and he took care of everything. It was heartbreaking enough without the kid knowing,
I cannot imagine how it would have been, had she known beforehand.
When she got home from school, I told her that he peacefully left us. She cried of course but I still think it was a better solution than having her think we should have maybe waited another day, or week or ........
One is always riddled with self doubt, I didn't want to spring this on my child too.
Either way, it's a difficult decision, you have all my sympathies.