The person covering your change of plans deserves acknowledgment, not an assumption of ease.

Changing your plans moves the difficulty rather than removing it. Somebody takes the shift, collects the child, or absorbs the extra work, and because they agreed pleasantly it becomes easy to file the whole thing as no trouble. Their evening was rearranged all the same, and their willingness is exactly what makes the cost invisible.

When someone covers for you, say out loud what it probably cost them and ask what it disrupted. Then find a way to return it soon, before the balance settles into a habit only one of you can see.