new bumper, now airbag light is on

I had a new front bumper put on my 06 grand caravan now the air bag light is on. is there a sensor or something in the grill that the shop did not put back on?

No sensor in the grill on that vehicle...
On most vehicles, the airbag light should come on for @6 seconds, and then go off if the system is working properly. If there is a fault or a problem in the system, the light will remain illuminated, or flash continuously. If the airbag light does not work properly, some vehicles have an audible tone that sounds indicating a problem with the airbag light system. When the light is on (or the tone is sounding), the airbag will NOT deploy, even in an accident. Most systems can only be diagnosed using a scanner designed for the airbag system, however some use flash codes to indicate the problem. The scanners at Auto Zone or the ones that sell for @ $50 will not access the airbag system, only the engine systems (check engine light).
This website gives you the procedure for diagnosing and resetting some systems without a scanner. Some vehicle manufacturers accommodate that (like Toyota, Lexus, Nissan, Infinity, Honda, Acura, Ford, Lincoln, Mazda & Mercury) and some require a scan tool. http://www.airbagsolutions.com/
Check out these websites also for more info on airbag systems and the light.
http://blog.airbagsolutions.com/archive/2007/11/18/why-is-my-airbag-light-on.what-should-i-do.aspx
http://www.airbagsolutions.com/resources.aspx
http://blog.airbagsolutions.com/
Check out this scanner for AIRBAG>>>It’s the cheapest one I’ve found!
http://www.airbagsolutions.com/scanner.aspx