In addition to the previous replies:
Try to prepare for situations where you know you're likely to become impatient and give yourself a little peptalk on what will happen, why you want to remain calm, and how you will respond when getting frustrated instead of snapping.
Like if a kid is really slow a tying their shoes, before asking them to put on their shoes, take a deep breath, tell yourself that "I want to give them the opportunity to practice without me stressing them out. We might be late, but it's just a matter of minutes, these things will happen. If I am getting annoyed I will take a deep breath and go wash my hands and smile at myself in the mirror because I didn't snap. If they want help I will be happy to explain how to do it as if it was the first time. They will do it their own way in their own time, but it will get done". Unclench your jaw and lower your shoulders, then slow your speaking voice to be extra calm and unstressed when entering the situation that will likely make you impatient.
Always repeat to yourself "They will do it their own way in their own time, but it will get done".