I don't know exact measurements or anything, but it sounds like it would definitely turn your umbrella inside out
If you weren't expecting it, it'd probably knock you over a little; maybe you wouldn't fall, but you'd stumble. I think a person could stay standing through it, depending on how strong they are. Is this for TAJ? I remember you saying your characters were on the small side because (I think) they weren't getting that much food and so were rather weak, so they might need to hold hands or hold onto each other to stand well. They'd probably need to squint to see.
Honestly, if they wanted to fight the dragon they'd have to get out of the area immediately affected by it's wings, because standing in that wind would take all the effort they had and they wouldn't be able to see it anyway. Could they climb in a tree or get some sort of elevation? That might help. If they aren't trained in that sort of thing, they would have to fight from a distance, and could probably only wound it enough to get by- unless they have a way you've thought of. Maybe one could try and get some elevation and throw stones in its eyes, blinding it? It's a bit of a stretch, but hey, what's fiction for?
Then again, it's fiction. There's magic and swords and dragons aren't real, so you could decide it's weaknesses. Maybe it's neck is really thin and easy to slice through. Or maybe you already know how they'll deal with it. Maybe they befriend it!
I hope this helps!