Grand kids have lots of ‘secrets’ they keep from their parents. You hold them. This gives you a certain ‘credit’ with your grandchildren.
This one might claim to be doing homework but really playing video games. She might say; “Grandma is helping me with my homework,” to mask reality.
Grandma says to the Grandchild; “Mute the sound so Mommy doesn’t hear…”
That one might sneak out of bed to eat cookies.
“Remember to wash your face and brush your teeth,” advises Grandma.
You do this to build up trust so that a few years later; when it matters, that Grand Child will come to you with those major issues.That Grand Child, who has come to respect your advice, rely on you, will come to you for help, when it matters