I'd like to push back on the idea that 6 year olds can't grasp the concept of commitment and therefor it's not worth trying to push. I worked in a program called philosophy for kids that dug into deep topics with 1st graders, and was blown away at the insights and understanding they displayed (as with everything there was variation from one kid to another). Different teaching approaches yield different results.
Defining a term in your own words and then saying why you think it is important is very different from taking that same term, introducing it via a developmentally appropriate story, asking guided questions, and then structuring activities to make personal connections to the theme.
For example, I plan on emphasizing the concept of integrity in my classroom this year. I'm not just going to write it on a piece of paper and then hold kids accountable to it. I'm going to do read them the story of the boy who cried wolf, ask them questions about why the town didn't believe him anymore, and the impact of not keeping your word. I'm going to have them brainstorm situations in their own life where someone kept their word, how that made them feel, and what they decided about that person afterwards, as well as the opposite where folks didn't keep their word, how that made them feel and how that impacted their relationship. I'm going to have them pick one of those stories to write more extensively about. I'm going to have them connect how keeping or not keeping their word might affect their ability to reach the goals they set for themselves earlier. I'm then going to define the term in student friendly language, have it posted on the walls, and refer back to it. Students will have points during the year where they'll self-reflect on their own level of integrity...blah blah blah
In my experiences working with kids, studying neuroscience and psychology, and teaching, I've found that just about anything is accessible to kids, given a thorough amount of scaffolding.
I applaud your effort to discuss serious values and moral issues with your kids, it's not meaningless and at the very least it creates the foundation for future conversations. Now about that extrinsic motivation tactic ($$$) I've got some readings to send you!