I had an amazing experience on Spirit Airlines today (6/25/2017) with my Peanut & Tree Nut Anaphylactic two year old.
They allowed my mom and I to pre board so we were able to thoroughly wipe down and put our seat cover on.
The staff asked passengers around us to save their nut snacks for their destination. In addition, people around us were very understanding. They also allowed us to sit with others in our family for no charge.
I just wanted to report a good experience.