(Strip Number 4289, Original Publication Date, 1 February 1983)
Panel 1: Mike asks if he can come to the convention. Unlike Elly when she was trying to keep the Martian from wanting to have a vacation in the sun, John is being honest when he tells him that it's simply a bunch of boring meetings and that he wouldn't have any fun.
Panel 2: He then tells him that he'll be the man of the house now that Daddy is away.
Panel 3: Mike's eyes bug out in existential horror as he imagines himself taking care of Lizzie, fixing up the house, stressing about bills and working from nine to five.
Panel 4: Since that seems like absolutely no fun at all, he amuses John by asking if he couldn't be oldest kid instead.
Summary: I sort of wish he could be oldest kid too. That's because he's Lizzie's primary caregiver and, as such, is going to be warped for life because he hadn't had a normal childhood.