Panel 1: We start things off with Elly bellowing that she doesn't feel like cooking tonight. This means that anyone living there will have to forage for him or herself if he or she wishes to eat.
Panel 2: This news delights Mike and Liz because it means one thing.
Panel 3: What it means is that Liz shouts "Snordasborg" (because she still has to do toddler jokes like mispronouncing words like 'smorgasbord') at John as he stares at them and their table loaded down with soda and snack foods.
Summary: The 'joke' is that the kids are BAD because they eat junk food and drink pop instead of making good food. Oh, if only someone knew how to cook good food and had the patience to teach them!