I asked this question a couple of weeks ago and got a lot of great responses. With all the responses, I called the airline with questions and looked on TSA website. Not to be rude and scare you, but every experience is different, every airline is dirrerent, and every security officer is different. So, here is my advice...
Listen to what every one posts, but don't take it to heart because your experience will probablly be totally different. Go to TSA website and look at what they say, your airline should have a link there as well. Print out the list from their site in case a security office gives you a problem.
I had a note on a prescription pad from my pediatrician that helped us when things were in question. She said to allow expressed breast milk or ready to use formula and childrens tylenol on flight. She told me to give my 4 month old and 2 year old the tylenol 30 minutes before the flight took off, and to make sure they were drinking a bottle or sippy cup on take off and landing.
They would not allow powder formula unless you mixed it in front of security, discarded what you did not mix, and let the baby drink right there. Leaving they let me take a sippy cup for my 2 yr old if we drank it, coming home they did not. They did not allow un-opened bottles of juice or nursery water even though TSA said you could take it. That is when they told me that if I had printed out the list they could look at it and verify it.
We took both kids on our laps...BIG MISTAKE!!! My husband and I could not sit together because of how many oxygen masks there are. We put the carrier in a bag and checked it on the way, but gate checked it coming back. Thank goodness for gate checking items like that. Gate check your carrier or stroller if you are taking either...it is worth it.
Both times I talked to a flight attendant on our flight before we boarded and they were all very eager to help and accomodate the best they could. The flight attendants were the best part of flying with the kids.
I will tell you one thing, everything I thought they would allow either was thrown away or flushed down the toilet. They would not allow anything over 4oz of liquid (breast milk or formula). My 2 year old came down with strep 2 days before we left and his medicine had to be kept cold-they did allow that. His decongestant was liquid, but prescription that I carried on and they allowed it on the way, but it expired the day before we came back and the security officer made me get rid of it goign through the checks coming back because he checked the expiration date. We almost got into a fist fight!
Good luck and have fun. Please don't take what I said as harsh, I just had a horrible experience a couple of weeks ago, but the MOM'S that responded to my question then were great which prepared me for the unexpected that we encountered.