These are slightly late but maybe you can use this ideal for another holiday or for fourth of july next year. I remembered us making them as I lurked around the web tonight and found this amazing site, Dollar Store Crafts, on Make and Takes. I can't wait to make the "tie-dyed" shirts this week with my kiddos. Our Dollar Store has had lots of shirts this year and my kids love to make shirts to wear.
Here they are in their firework shorts. I had them draw their fireworks then spread the paint with a brush. I then helped them write "I (heart) fireworks" on the designs. I then added their names and the year to the sleeves.