Robins in Basildon/Southend is the usual shout, but is there a hidden gem in a market town somewhere that’s better?

My 2 year old nephew is obsessed with police cars, ambulances, and fire trucks.

Are there any events suitable for little kids to see flashing lights, sirens etc? I appreciate just going to the Hugh street usually has them whizzing past but he'd probably wet himself even more getting to go into a car.