Aw ohseedee, it doesn't sound silly AT ALL! I think most people would be nervous about that, even people without anxiety issues etc!

I think it's incredible that you're determined to do it even though it scares you. I'm sure it will be fine, you don't have to be chatty or anything, you could perhaps come up with some questions like "are you enjoying the fair?" "what have you bought/been on?" so you have some things to say if you feel akward about the quietness. But I think even just being quiet will be fine, you're meant to be concentrating on the painting afteral, so I doubt people will be trying to distract you too much with chit chat. And the kids can't really move much when you're painting so it's probably better if they don't talk lots, lol.

I really think you'll be fine. Just, if you like, try to think of some ideas of things to say (like the examples I gave). For me if I feel nervous about something like that it helps me to have an idea of what I might say etc. But really I'm sure there will be no pressure to talk and you'll do just fine!