A few more questions about the scenario.

1) Am I making my stand outside?
It would certainly be easier to set up the main perimeter inside the mall. Have all the kids/others retreat to a higher floor, while you fight the zombies as they file in though a set of doors. Waves of 3 or 4 zombies are a lot easier to handle than a horde, and that would bring the added bonus of each dead zombie adding to the ever-growing pile of corpses they'd have to climb over to get to you.

2) Zombies usually only come out at night, so what kind of light sources are around?
Depending on what light sources are available, you could likely set up a barricade with just floodlights or very strong flashlights (1M candle power flashlights are incredibly bright).

3) Does this mall have a gas station in the parking lot?
If you could get some of the zombies near the fuel tanks, that would be an easy way to get rid of a lot of them. Shoot the fuel tanks.

And if all else fails, feed them Mentos and Diet Coke.