I'll be traveling with my daughter to Krakow where we will stay near the square. Any suggestions for gluten free restaurants?
Not specifically, but I don't think you'll have trouble finding safe vegetables, omelets, and grilled meats at most places. Servers working near the main square, and especially younger staff, are likely to speak English. Kebab stands are a popular fast-food option where you can pretty well see what you are getting.
There are some gluten fee websites where travel is addressed and restaurants are recommended. I would try looking at those. On a quick search of one of those websites, one of the posters pointed out that a popular gluten free company is based out of Poland.
My sister is a vegetarian and when we went to Poland, this was not a problem. Many restaurants, and even the street side sandwich shops, had "Vegetariansky" options. I know this is very different from gluten free but at least you know they are open to dealing with different food preferences. Most of the menus we encountered were varied enough that I think you could have a good meal while avoiding the gluten options, as Laura said.