Place it near the end of a short edit, just after the helpful moment, then follow it with Kids Cheering for a bright finish. If the favour was unexpected, start with Oh My God Wow before the thank-you so the reaction leads naturally into the gratitude.
About this sound
This is a short spoken French thank-you, lasting just over a second, with a clear, friendly voice saying merci. It feels warm and polite rather than formal, like a quick smile in words, and it lands as a light, charming way to show gratitude without making a big moment of it.