Here's an email response I had that may help...

Perfect...almost.

That's exactly how you find p-hat but you always use the decimal form of it.

So 21/122 = .172, and that's p-hat. So then for the formula, you'll have .172 +/- 1.645(square root((.172)(1-.172)/122).

To actually calculate it, use your calculator--STAT-->TESTS-->ONE PROP Z-INT. When the next screen pops up enter x (the number of successes, or in this case, number of kids who said "yes"), n (sample size), and the confidence level, as a decimal.