I'm sure you'll be relieved to hear that no actual caterpillars were harmed in the testing of this recipe.
2 cups grated cheddar
1 cup grated Swiss
1/4 cup grated Parmesan
8 cups uncooked rotini, (but they'll always be caterpillars to us)
3 tbsp butter
1/4 cup all-purpose flour
2 garlic cloves, squished (or more, less or none)
2 tsp mustard, (Dijon, if you have it)
3 cups milk
1/2 tsp salt
1/4 tsp black pepper
With (clean) bare hands, have your child toss together the cheeses in a large bowl. A spoon or fork can also be used, but that wouldn't be nearly as much fun. Remove about 1 cup (250 ml) of the cheese mixture to a small bowl (this will be sprinked on top later) and set both bowls of cheese aside.
Meanwhile, bring a very large pot of water to a boil, add the rotini, and cook until tender but not mushy. Drain, then run cold water over the pasta to rinse, and drain thoroughly. Dump it all back into the pot.
In a medium saucepan, melt the butter over medium heat. Add the flour, garlic and mustard, and cook, stirring for a couple of minutes. Pour the milk in gradually while stirring to keep the mixture smooth. Cook over medium heat, stirring constantly, until the sauce thickens. Remove from heat. Now have your young helper toss the large amount of cheese mixture into the sauce - one handful at a time - stirring as it melts. Don't cook the sauce after you've added the cheese or it may become stringy. Season with salt and pepper.
Pour the cheese sauce onto the cooked and drained pasta in the pot, and toss until evenly coated. Scoop into a greased 9 x 13 in. (22 x 33 cm) baking pan, and sprinkle the reserved cheese mixture over the top. Bake at 350°F (180°C) for 20 to 30 minutes, until it is thoroughly heated and the cheese on top is melted and bubbling.