"Why didn't you tell him the truth?"
"You didn't tell your grandma we were going to a dangerous underwater city, did you?"
"I kinda sorta... didn't tell her anything?"
"Webby, that's irresponsible! She'll be worried sick! Call your grandma this instant, and tell her that you are spending the night at a friends house, okay?

Lying, it's the responsible thing to do."

A great lesson for the kids watching this show!

—
DuckTales Season 1 Episode 2