I travelled in July - CPH, SEA, LAX, ORD - with my then 3 month old, and had a similar expeirence in all the airports -- no problem. Arriving in Seattle they made us go through the extra agriculture x-ray because of the formula (food?), but that was it. I even had bottles filled with boiled water and it wasn't a problem (since they can't easily boil water for you on the plane). What I did was put all the bottles - some with water, some with pre-mixed formula - and unopened packages of pre-mixed formula in a big ziploc back, so I could easily pull it out to show them -- although at some of the airports, they didn't even care and once I told them, they said to just leave it in the bag.