Gift to Firefighters

I recently got my son a new car seat and took it to a local fire station for them to install. They were all so kind, and not only installed the car seat but showed me all the bells and whistles. All of the firemen were so nice to my son, and it really touched my heart. I plan on giving them a thank-you card with a photo of my son in his new car seat, but would like to give them something else to say thanks - donuts maybe? Another sweet treat? I’m up for your suggestions.