"Watch me Mommy"

Spoke to Olivia on the phone tonight. Dan and her were at the playground. In her four year old mind, she can't quite grasp that Mommy can't see her through the phone. She kept telling me to 'watch me, Mommy' while she went down the slide or "watch me Mommy" as she climbed up the ladder, on and on. I kept trying to tell her that Mommy can only hear her over the phone not see her. Then I tried logic on her, asking could she see me? If she can't see me, then I can't see her. No avail, right before she said goodbye, she yelled, "watch me Mommy"...sigh. Perhaps that's a concept that only 4 1/2 year olds grasp?