Speaking with the experience of my daughter (now 3 months from 5yrs old) and her friends, the ability to do more than just pretend to understand abstract thoughts seems to have hit right around the time that they began to try out more advanced lies. For example: "Mommy (who already left) promised I could do something (that mommy would clearly not promise)" The concepts just need to be framed in terms they want to understand. For my daughter the threshold was around 4.5 yrs. Most recent example, light. I gave her a flashlight a while back, she had a good time playing with focusing the beam and moving it around. Later I moved onto the Sun being the source of light like the flashlight. Last week her teacher sent her home with the question: "why is the sky blue?". One trip to the Discovery store for a prism later and I showed her all the colors in sunlight. I then told her that air reflected one of them to her to get that blue color (she gets reflection...loves mirrors). She chimed in, 'So grass reflects green?'. Much warm fuzzies for her geek dad. Small negative aspect: On getting home she promptly compared to her flashlight's light through the prism resulting in an immediate request for a better flashlight that is like the sun. Followup I've asked her to give her teacher the question: "why does air reflect blue?" Wish I could be there to videotape her teachers look.
Treat your work visit as the point to lay the foundation for good questions by the children later on. If possible send them home with a small fun toy that demonstrates parts of the concepts you're trying to show them. That way they can mentally creep up the concepts when the play with the toys...and telling the doubters raising objections to your planned trip to google on 'Montessori' (and get out of your way).