How do you address your kids teachers?

I'd assume that (in most cases with teachers anyway). It depends on the person too. It's about a general impression I guess. Age, posture, way of speaking, things like that play a role. The position of primary school or high school teachers doesn't automatically make me switch to last names, but I could imagine that I would with some.

Then I say, "Hello [firstname] [lastname]. Nice to meet you." :)
I won't need the name for the rest of the conversation anyway.
Since they mentioned their first name, they shouldn't have any problem if people called them just that, but I would honestly use whatever they said in my first reaction.

I'm not sure using first name necessarily means it's okay to use it. Just my opinion :)

Listen here toots jk

Just like with everyone, I address them the way they got introduced to me or how they introduced themselves, but I avoid unnecessarily using people's names when speaking to them anyway.

Scub - if you're sending them an email and they don't know who you are - will you start with first or last name?

@bbcjsv I go with Mr Mrs. or Ms unless I know them. Even after I know them it will depend on why I'm emailing

Depends on the teacher and their level of common courtesy

Sometimes you feel like saying that don't you lol

What if they introduce with first and last name?