That is so great. Your boy looks so happy, like he will look when he discovers that girls aren't icky.
Firefighters are usually pretty friendly types and most probably remember what it was like when they were knee high and had the same enthusiasm your son has. It's their turn to give back a little and make a kid's day. I remember going down the street to my local fire station to admire the shiny red trucks. The guys would give us "Wagon Wheels", which to the unaware are like Mallomars described in Gresch's post about "mmmmmm".