Writing a story where my main characters get trapped in a mall for a week and need your ideas!

One could be hiding in a Halloween type store and they jump out at another character in some sort of Halloween mask like maybe a William Shatner mask or something else you devised.
One could play a cruel joke that involves them looking like they were stabbed or something.
One could spray another with a super soaker
They could always pull the prank with shaving cream when they when one falls asleep or something
Put hot sauce in a class of milk

does that help?

I love the idea. (I wish I thought of it!)

However, what your story is missing a main conflict. We've got the characters, and the setting (the mall) but there is no problem or conflict. What are the main characters trying to accomplish? Do they want to escape the mall? Are they trying to pull the "best prank ever?" Is someone dangerous locked in the mall with them? Are they there hiding from someone who wants to hurt them? Are they simply trying to survive until the mall is unlocked? Etc.

Ideas for you:

1.Don't some malls have stores that sell motorcycles? Zooming through the mall hallways on a motorcycle would be cool.

2.Candy store!

3.Get money from the bottom of the fountain ("Wow, that's a total of two thousand dollars in coins! Who the heck throws this much into a pool of water?!")

4.Maybe a night guard (just one) who shows up at a certain time each day, leading to narrow escapes (hiding behind the bookshelf in the library or in the clothes racks)

5.Going to the bookstore and hiding all the books they hate behind the shelves so no one can read them

6.A pet store!

Prank ideas....
IDK.
Maybe there's a waterslide at the pool that they get working (a huge one!). One person makes what looks like a goblin or troll out of clothes and halloween decorations and puts it at the bottom of the slide. (Whoever slides down will get freaked out when they hit into some weird ghoul thing at the bottom!)

Tricking someone into attempting to go down the "up" escalator

Taking a book someone REALLY dislikes out of the store and putting it under their pillow every night. When they wake up every morning they'll be all like "OMG THIS BOOK'S FOLLOWING ME."

-Yeah, I'm not a prankster-