"What's the matter -- d'you have ants in your pants?"
To have "ants in one's pants" is a metaphor or idiom for a range of nervous or agitated emotions, leaving one unable to sit or stand still. It is especially applied to children, particularly those whose energy, once described as "fidgety", might now be termed "hyperactivity". The children so labeled might describe themselves as nervous, anxious, bored, or just eager to move on to a new activity.

It is quite possible, in certain outdoor settings, to actually get ants in one's pants. The sensation is not comfortable in the least, and indeed precipitates a certain degree of twitching. The vivid metaphor finds its way also into traditional children's rhyme, viz.:

You've got ants in the pants
And they make you do the boogie dance
All the way to France
In your underpants!