I like to tuck 1/2 a Valium or a Xanax inside a jellybean or a Junior Mint, and then just offer it next to any kind I'm seated next to at the theater or on a plane.
It's usually better to make nice to the parents first, so you don't get blocked by that whole "never take candy from a stranger thing."
It also works tucked inside a suppository when you go home with the wrong trick. Only it's better to use 2 Ambiens instead of 1/2 a Valium. The minute he starts yawning, you just say, "Oh well, I guess you're too tired. Why don't we take a rain check?"