1) Why does one have to take off his tallis gadol when entering a bathroom and not a tallis katan?
2) Does one need to remove his kittel before entering the bathroom?
1. The difference between the two is that a tallis katan is worn all day and considered an article of clothing, therefore we may wear it when entering the bathroom. A tallis gadol on the other hand is worn primarily when davening, therefore it is considered a garment of mitzvah.
2. One should remove his kittel before entering the bathroom.
1. Shulchan Aruch O:CH 21-3.
2. Mishna Berura 21-14.