It is so easy to make cupcakes or cakes stunning. All you need is a little imagination and some time. There are places one can buy sugar flowers. I highly recommend buying them, but making them can be fun...especially for kids.
The ones in this image were purchased from http://www.fancyflours.com/. A great little site with fun and beautiful decorations. To make the leaves, I used left over frosting which I added green to. The tip is a leaf tip. Practice makes perfect when it comes to piping. You can find disposable bags and a variety of tips at http://www.fancyflours.com/ or http://www.michaels.com/.
You can use a recipe for cake to make cupcakes. However I would add more fat (butter or oil) to make sure the little ones don't dry out in the oven. If you are not much of a baker, the pre-mixed cake mixes are great. And for the frosting I would recommend making your own. A great recipe mixes soft unsalted butter with confectioner's sugar. I never give measurements because you should decide how sweet you want it. But generally it's 2 sticks butter to every 4 cups confectioner's sugar. For those with no patience or time, buying a tub of pre-made icing works. But I would try adding two sticks of soft butter and whipping it. It will give you a smoother and more "homemade" flavor.