Two good substitutes:
Lemon or lime juice. Depending how much liquid you need, water it down and sweeten it, honey would be excellent. Lime juice is better because it's less acidic, and it goes really well with chicken, so much so that you will never miss the wine! You can add some of the zest too.
Vinegar. Most kinds will do well, but water it down so it's not too strong. Best is wine vinegar (of course) or cider vinegar, just avoid malt vinegar and household vinegar
