That's great, Izzie! They'll love it! I would have to admit that I've never had the opportunity to try this recipe in a super muggy climate, but when I lived near Lake Michigan I had friends who had great success using a similar recipe. It was quite humid there. Here in eastern Washington it's rarely "humid" by most people's standards. We like to do these either early in the morning, or on a rainy day in between showers, as they seem to work best when the air is moist. Hot, sunny, dry days are no good at all.
So, I'd say you'll be fine! There are several YouTube videos demonstrating the technique for making the bubbles, so you might want to check some out... It takes a bit of practice, but is totally worth it!
Good luck, and let me know if you have any other questions... I'm happy to help if I can.