What a fun way to introduce wild foods to your kids.. how great that they get to have all these experiences in nature with you :) Yeah definitely a good idea to know for sure a mushroom is edible before feeding it to them :) Maybe there are mushroom foragers in your area that do workshops or mushroom walks? I find having a friend helping me identify mushrooms is easier than reading in a book. But there's always more to learn. As far as the marshland I don't really know the answer to that question to be honest. I have not spent a lot of time around marshes. My guess is that if there are dead trees in the marsh there might be mushrooms growing on them even if it is too wet below... but I am not really sure! I would just explore and find out whats growing there!