A social story can help prepare your child for an activity or event. Here's a free 4th of July social story from Positively Autism: http://www.positivelyautism.com/downloads/4thofJulysocialskillstory.pdf
Parent Tips: Surviving 4th of July Fireworks - http://www.pathfindersforautism.org/articles/view/parent-tips-surviving-4th-of-july-fireworks
10 Tips for Enjoying Fireworks on the 4th of July with Autism - http://www.abpathfinder.com/fireworkswithautism/