The most important lesson about Grilled Cheese that I have learned is that you can buy a mix of expensive cheese, get a nice fresh loaf of sourdough bread, high quality grass fed butter. You can really make an exquisite, amazing, grilled cheese that would cost $25 at a mediocre restaurant with a side of fries. However, a 4 year old will prefer one made out of kraft singles on white.
As a near-fifty year old who has been making sourdough for 6 years, makes homemade mayo with a grated garlic clove and freshly squeezed lemons every couple weeks, and keeps a stash of fine cheeses readily available for all occasions - I'm with the 4 year old. White bread, 2 slices of american, butter - it's hard to beat the sheer comfort, texture, flavor, gooeyness, and simplicity of the classic.