Your first option is to back out now before it's too late. It's far too late to be able to plan out a "impromptu" routine without any equipment on the spot in that amount of time. This may sound depressing, but it is the most professional thing you can do right now for you and for those children. If you cannot give those children a 110% of your magical entertainment, then why bother? You don't have the necessary equipment, you don't have the amount of time to prepare a brand new routine, and you haven't rehearsed these "impromptu" tricks well enough to formulate a decent routine. I see it as a no win situation. You're walking into a gun fight with a butter knife my friend, the outcome for victory is not looking good at all.
Your second option is to go on a whim, and try looking for one of those magic kits that they try to sell to children. It may be a bit humiliating, but you will be surprised by the amount of material that you can actually perform with it professionally. It helps you look the part, and adds a hint of silliness to it all. You'll be familiar with the equipment, instead of coming with napkins, and newspaper that will look rather boring.
Your third option, which I highly don't recommend is to:
1) Build your own magical coloring book. If you ever had one to use and perform with, you should know the concept and how easy it is to make one. Although, you will probably have to perform some labor if you know what I mean.
2) Rope. Rope magic, no matter where, who, how, what, when, then... you get my drift. If you know the tricks, and you have a story or patter, you have magic.
3) Perform some mystical science experiments. I may have lost you on this one, but trust me, science and magic go way back. For example:
a) Find a cup, drill a hole into it near the bottom. Fill it with water, (make sure your finger is over the hole) and put a piece of cardboard over the cup. Voila! The water won't fall out due to a little physics and to their young minds, that's magic. Snap your fingers and let go of the hole and boom, the water falls.
b) Buy a bottle of water with the brand name Fiji. Place this into a freezer undisturbed with no movement at all! I cannot stress this one enough. Leave it in there for a day and you'll notice that the water still has not frozen. Now, witness the magic by giving it a little shake. The water will then begin to freeze before your very eyes. That's another scientific discovery known as viscosity and density. http://www.youtube.com/watch?v=4EABdAEt_fM
Look around 3:56 for the routine that you can do for example a.