Do you think it is okay for kids to greet adults by their first names?

They should say Mr./Mrs. unless that person requests something else. People should call other people what they want to be called. 

I think the adult should tell them what they should greet them by.

I am teaching my children to call adults Mr./Ms./Mrs. "last name", unless the adult tells them to call them by their first name. I really have no belief one way or the other. 

It's sad to say, but very few kids are taught respect to their elders. probably from the left, the way you see them act on the news.

Like it when respect is shown

i would think it depends on who those adults are

I was raised to show respect to my elders by addressing them by mr./mrs./miss so and so. I tried raising my children with the same manners. Now that they're adults they appreciate their upbringing.

"I think children should call adults by their title until otherwise agreed upon."