There is nothing wrong with adding some art work to the image, but once again, remember these are very status conscious 13 year old kids, who won’t use anything that makes them look anything but cool. A reliable party favor specialist should be able to have their graphic artist create something that is subtle, yet interesting enough to appeal to the 13 year old mind. The absolute worst thing you can do is put a picture of your child on a party favor. No one will use it and the chances are that if anyone does use it, it will be because they have drawn a mustache or beard on the picture and they think it is funny. Not exactly how you want you child’s special day to be remembered.
Another thing to keep in mind when imprinting is the more colors you use the more expensive the item will be. The image may look really cool in 5 colors but the cost could get prohibitive. Again a reliable party favor specialist should be able to create something using only one color, some halftones plus incorporating the color of the item into the design that will make it feel like more then one color but not add to your bottom line.