i get tackled if i go outside with any kind of food in my hands. Even though all my birds have feed 24/7, they love extra treats. i think the only way to stop it is to not go out with any food in your hands you don't want to give away.
Teach them not to take food from you that you are not giving to them. I don't allow mine to fly at me especially at my face. Mine peck at my rubber boots but it doesn't hurt. They also peck at my fingers but they are wanting more treats because I am just not fast enough passing the treats out. If mine are doing something that I don't want them to do, I bump their breast with my fingers making them back up. I started doing that when they were days old. So now I rarely have an issue of one getting too aggressive. Granted mine are still young, 9-12 weeks, so I will wait and see what issues I have when the hormones hit in the roosters. They also know that when I snap my fingers and say no that it means to stop being aggressive towards each other. They are trainable, it just takes work and time. If I had small children, it would be time I would gladly put in to keep my children safe. Just my thoughts and what is working for me.