The Phineas and Ferb TheoryHere it is, the Phineas and Ferb Theory:More Like This
The events taking place in the show are all the delusions of a group of kids in a children's psychiatric facility.
That's why the parents never see anything and why everything is so easy to do in that world. In reality, Phineas and Ferb's inventions are made of toys. The reason nobody ever gets hurt on anything is because (since they're locked up) the toys their inventions are made from are childproof to prevent their use as a weapon. The reason they "disappear" at the end of every day around the same time is because they have scheduled time to play with them.
The reason the parents go away so often during the episodes is because, while they visit as often as possible, they aren't allowed to be with their children all day. The kid's minds make the grocery excuse to explain why the adults are so often absent.
Phineas is Schitzophrenic and detached from reality. He's so happy all the time because of the mood stabilizer's he has to ta