>>105031719The boys specifically do not realize their mother will be upset with their antics, though this is winked at from time to time. This was specifically done because there were so many too clever kid characters on tv and the creators wanted Phineas and Ferb to be nice.
Kinda robbed Phineas of his funny "8 year old PT Barnum" characterization which is a shame.
Also the boys help Cadance with Jeremy all the time. All she'd have to do is ask, so why blackmail them?