Different rules apply if travelling with kiddies, IIRC - from TSA's "Travelling with children" page (http://www.tsa.gov/travelers/airtrav...n/index.shtm):

"Baby Formula, Breast Milk, Juice, and Other Liquids
Medications, baby formula and food, breast milk, and juice are allowed in reasonable quantities exceeding three ounces and are not required to be in the zip-top bag. Declare these items for inspection at the checkpoint. Click here to learn more about 3-1-1

All items including formula, breast milk, and juice will be inspected, however, you or your baby or toddler will not be asked to test or taste breast milk, formula, or juice. Our Security Officers may test liquid exemptions (exempt items more than 3 ounces) for explosives.

» Click here to read about traveling with formula, breast milk, juice, and baby food."

From a quick online search, it seems like it could be justified in carryon under either child's formula or medical necessity exceptions (depending on why it's being used). With the caveat that I am NOT a screener or other TSA employee, I would say declare it prior to screening per TSA's instructions and you *SHOULD* be good to go - provided your screener doesn't decide to make up his own rules. In which case, call for a supervisor to clear you and file a complaint after getting through screening. Having a copy of the TSA webpage in hand may or may not be of use, but probably couldn't hurt.

If you are transporting the Pediasure and NOT travelling with kids, they'll tell you "No exception, check it."