I have a dessert I make that has Creme de Menthe in the frosting, 2 tablespoons for frosting for a 9 X 11 pan of brownies. I thought about subsituting mint extract for the Creme de Menthe so my kids wouldn't get alcohol. The mint extract had a much higher percentage alcohol in it so I stayed with the liquor. If you are worried about alcohol in food, check out your vanilla which is 35% alcohol, or 70 proof, which I am sure is higher than Kahlua. It is eye opening when you start comparing the alcohol content of some common things.
Bottom line, go with the Kahlua.