Parent Hacks has a simple recipe for mac & cheese that is as quick as the box stuff, but more healthy:

Cook macaroni (if you can get a hold of the whole wheat kind, so much the better). When done, drain, return to the pot, and add a generous pat of butter. Once the butter melts, sprinkle in a tablespoon or so of flour. Use your fingers to sprinkle in the flour so it doesn’t clump in one spot. Stir well. Add a splash of milk, and then some shredded cheese (cheddar, or a mix of cheddar and jack). Stir till everything’s nicely melted. Add a little more milk if your kids like things saucy.

Parent Hacks is one of the great parenting sites- stop over and visit when you get the opportunity.