I was wondering if the glass baby food jars will burst (due to pessure changes) on an airplane. Also, does TSA give you a hard time about bringing them in carry on? thanks

Never had a problem. Those jars are pretty tough. They are also very small, absolutely no trouble from the TSA.

Maximum cabin altitude is about 8000 feet...you can get higher than that by visiting Bryce Canyon or driving I-70 across Colorado.

I have seen the sad sight of the TSA agent pouring out the beverage from a crying toddler's sippy cup more than once.

I do not think you can bring baby food jars on the plane unless they are in a quart size ziplock. I haven't been able to bring small yogurts or applesauce, for example.

Baby food is an exception. Can be over 3 oz in "reasonable quantities". Liquids in a sippy cup, etc are something else and like any other liquids. They don't have to be in a baggie. Just declare them in advance [and suggest just taking unopened ones on the plane].

And yes, those jars are pretty tough.

see tsa.gov

There are special rules for baby food. See the website above.

Does anyone know when a baby stops being a baby for these purposes? I have a 3 year old and would like to bring juice for him on the plane. Do you think they will allow that? I know I can buy it after security but he likes sports top drinks and I don't want to mess around with pouring from a bigger bottle into a sippy cup. Any experience?

TSA doesn't care about age per se. Baby food and formula are allowed; juice is like another liquid and subject to the 3 oz rule.