Cute theme idea! Oriental Trading (
www.orientaltrading.com) has yellow plastic construction hats for about 50 cents each - you could personalize these using masking tape & a sharpie. You could take black plastic tableclothes and using masking tape, make hash marks to represent the road dividers. Home Depot would probably donate those little aprons that they give out at their kid classes. I would also use all of your child's trucks, cars, etc. for decoration. You could make signs like "Men At Work" "Can We Fix It?"
The great thing about the aprons and the hard hats is that they can double as party favors. If you felt like you needed to do more for goody bags, Dollar Tree sometimes has cheap tool boxes. You could fill these w/ Tonka fruit snacks, a bandana (to wipe the grime of a hard day off), plastic hammer or tools, etc.
As far as games - I would not do a lot of structured games due to the ages of the kids but maybe have stations. A coloring station where they can color pages from the Tonka website or a buy some cheapo coloring books from the dollar store. Maybe a station where the parents help - you could buy unpainted birdhouses from Michael's or Hobby Lobby. Set out tempura paints & have the parents help (great activity for the garage). Or you could have an "Excavation" area w/ the wading pool in the garage. Fill w/ sand or dirt or shredded paper and bury Matchbox cars to be found. You could make a bean bag toss game or Oriental Trading also has a construction bean bag toss game for $15. Or you could make a Bob the Builder version of Pin the Tail on the Donkey. Find a poster of Bob and make construction paper hammers or whatever & play "Pin the Hammer on Bob."
Have a fun party!!
