I have been to the Melting Pot and Simply Fondue and have never seen children there... doesn't mean they arent welcome, just was a more romanticy place both times we went to both places. Plus its expensive and is a long meal.... Just been my experience when we go. We usually go for Vday or our anniversary, its a special event.
They bring you the foods uncooked, and you cook them in your broth or oil or whatever you choose. It is usually a 3 course meal, with a cheese and bread to start with, meats and broth or oil for entree, and chocolate and fruits/cakes for dessert. It takes a long time... but is what we like about it! Its a dining adventure and can be very very romantic =) We love going, but its pretty expensive and usually you have to make reservations, so we don't go often =)
I would just call and ask them about children, I'm sure each restaurant handles things a little differently. We always order a combination dinner that includes all 3 courses, but I would think you could just order the cheese appetizer... ? I'd just call and ask =)
We LOVE fondue =) Highly recommend it!