You can take liquids for a toddler in "reasonable" quantities through security. They shouldn't make you test it. If they do, ask for a supervisor. They might want to test it for explosives (takes all of 5 minutes).

I wasn't keen on powdered "toddler" milk at that age because of the sugar content. UHT milk (I think what you're calling "aseptic") is popular in Europe but I'm not a big fan. Be sure you try out any milk at home first, so they don't balk at the taste on the day.

I was also in the no-milk-while-flying camp with my toddlers. Skipping it is not a big deal for a few hours but bring it if it will make your trip easier with them. Be sure to transition them to sippy cups before leaving. Much easier to wash and carry on a long trip like this. You'll also find it's easier all around. 14 month olds don't need traditional bottles with artificial nipples that can be a pain to clean.