As artists, it's easy to get caught up in the mentality of doing art at your desk. Even in the classroom with active kids, this is often the case, if not moreso. I'm a wholehearted advocate for playing outside - yep, even in the rain! This goes for making art too!
With kids, the process is more important than the product. This is important to keep in mind when making art outside, especially if the weather isn't cooperating. No one is looking for perfection. Heck, a good portion of my art doesn't come out how I envisioned, but I just plow ahead anyway. If it really isn't what I was looking for, I chalk it up as a learning experience and do it again! This can be especially frustrating for kids, but keeping it fun helps alleviate this.
Last school year I had the opportunity to do two fun outdoor art events for kids. One was with a large Girl Scout troop. Due to unforeseen and rather unforgiving circumstances we were unexpectedly outside in the rain for a painting activity. The parents were understandably unhappy with the situation, but the kids...they gave it their all! Digging deep into my training at Woodland Park Zoo as an informal educator, I introduced the girls to being mindful of their presence in nature - being as silent as they could, enjoying the sounds around them, and being part of the outdoors themselves. Our project was watercolor painting...in the rain! Despite a few grumbles ("I don't like the cold!", "I forgot my coat!" - I assure you it was 60F and lightly sprinkling, no one was in any real discomfort here) they produced some awesome art, and for the most part they were really into it! What does happen when the art I make doesn't turn out how I expect? How does rain change my painting? Can I work with nature to make something great? They went away with some beautiful pieces of art, and perhaps a new connection to the natural world.