Seems like just about every event has them. At family based events especially. Parents tend to let their kids wander, knowing they are in safe/good company. Therefore they visit the entertainment areas by themselves, especially when we bring toy boxes. :-) They return over and over and over, run off with props, pop in on other guests in the booth, or just like to push the buttons. You almost always learn there names and let out a big breath when they get fulfilled and move on.
Though tempting, giving them lots of sugar and caffeine is usually avoided. Many times we ask them to go get their brother, sister, or mom to come take some pictures with them. Or tell them that one of the shots is really good, and they should show their parents right away. I've even had a few that I give them the prints and they hand them to the guest as they come out of the booth for me, they really feel appreciated helping out.
So what are some of your techniques for working with them?