Two senior-citizombies kiss passionately. Nothing else.

All of this is relatively cartoon-ish violence only:

A tall shadowy man is fired at by a ray.

There's a space battle, ships are fired at by rays.

A robot is pantsed, and to men are sent smashing to the ground, but are unharmed.

A vampire-like-character is hit in the face with kangaroo legs (nothing shown, just cartoon violence)

A man smashes through a window, glass shattering. No blood nor is there any real violence.

There is a large skirmish in which zombie-like characters transform each other by slamming their palm on their faces.

Numbuh 5 attacks her sister by jumping on her back, hitting her jet boots with a wrench.

The Toiletnator, as a senior-citizombie, is hit many times by objects, and attacked my ninjas. Only comedic.

Numbuh One's dad transforms into Numbuh Zero, and it looks a bit painful.

The Delightful Children try to kill Numbuh One and his dad with a ray gun. They are stopped almost immediately, and it's not violent nor is it actually stated they want them dead. They use the word "eliminate."

Numbuh 362 duels with a Senior-Citizombie, they both don't get hit.

Numbuh One is forced to fight his five friends as citizombies, and then fights the Delightful Children. No blood, not very violent.

Numbuh 2, still half citizombie, kicks Numbuh One in the face comedically.

Grandfather gets hit by a giant moon base, which is lighten on fire by the speed it is at. It is shown from a pan shot, and he emerges unharmed. Numbuh 0 and Grandfather are fired at by a ray, exactly like when Numbuh 0 first transformed.

None.

Some kids drink soda like alcohol.

The transformation to citizombies and the citizombies themselves may be frightening to small children.