When my middle daughter was a teenager, I discovered she was struggling with trusting me and her dad. I couldn't understand where it was coming from. I believed I'd always been honest with her, had modeled honesty with friends, neighbors, family, etc. Finally after many talks, she said "When I was eight you promised to take me to get ice cream. Then you didn't."
Whew. My first knee-jerk reaction was indignation. I could hardly believe this one incident could be the reason my daughter felt the way she did. I had always prided myself with being super honest with my kids. To the point of them saying they wanted things more sugar coated! lol
What I failed to see at first was there was probably several times in her childhood I had made a promise like that one, and broken it. I probably never considered it a very big deal and likely never thought twice about it. I was wrong, and I learned the hard way how trust between a parent and child really work. I learned expecting your children to trust you is not just about being a truthful person. It requires that you ALWAYS mean what you say, and say what you mean. It means you ALWAYS do what you say you will, and don't do what you say you won't. It sounds simple. It's not always so easy, or so black and white.
I came to practice a new way of communicating with my kids that did not give guarantees or promises lightly. If there was a possibility of things changing, or if I felt I couldn't fully commit to something, I would be truthful and say so. It was better to have them disappointed that I couldn't say 'yes' for sure in some cases but still have them trust my word, rather than saying yes in the moment to spare their feelings (aka wrath) and have my word lose value. From then on I was much more guarded with my word than I was before and it took some growing pains for us all to become comfortable with this new way of honesty in our family. I am so grateful for my daughter's help in letting me understand this concept so well.
What you can do...
Instead of choosing to say 'I promise...', be super honest with your child. “I know you really want to have a play date with Sarah this weekend and we’ll do our best to make that happen. Please remember that sometimes unexpected things come up, so I can’t guarantee that it will happen this weekend.” Be sure you really are doing your best if you say you will too. Keeping your word builds trust and breaking it deteriorates your connection, so be careful what you say, and then live up to your word as much as humanly possible.
One more note on this, if you do break your word, acknowledge it and apologize to your child. Remember, you’re teaching your kids how to behave when they fail to live up to their word. Breaking our word is something we all do at one time or another. And even if it’s over something that seems trivial to you, it could matter a lot to your child. So do your best to be an example of honesty, and when you’re not, step up and take responsibility for your failure.