The birthday venue is home turf, and you have to rustle up a theme and some visuals to put everybody in a party mood. Champagne, oysters and candlelight won’t do for a kids’ party. <br>That takes some theatrical skills, an eye for color — the brighter the better — and a hefty dose of imagination, an unusual focal point, an engage-the-unruly-guests activity, or a talent for doing a lot with a little to save your budget and the day.