Panel 1: We begin things with John spending Father's Day cleaning out the Magic Crawlspace. He smiles as he reaches into a box labeled "Misc. and Stuff" and thought-bubbles "Well, what do you know?"
Panel 2: As he holds up a model kit for a boat, he reminds himself that he bought it but never built it.
Panel 3: As he spreads everything out on a table, Mike asks him what it is; he tells him that it's a model boat kit that he thought he'd build today.
Panel 4: Mike says that he wants to help; John says that he's sure that there's something he can do.
Panel 5: Since Mike is an incredibly average child, he accidentally gets glue on the plans.
Panel 6: Lizzie is ambulatory and talking today and signals her intention to join in by saying "I wanna!! Me do it, too!!"; since John isn't quite sure what that means, he says "Uhhhhh....okay."
Panel 7: Mike holds up a rail and asks "Like this, Daddy?"; since John is way cooler about things than Elly, he says "Why not?"
Panel 8: Since he has yet to be fully indoctrinated into the Patented Elly Patterson "Avoid children" school of parenting, John only frowns slightly as he thanks Lizzie for breaking something he sort of needed.
Panel 9: An enthused Mike asks if they're finished; John's saying that they're calling it finished would probably go right over the head of the idiot bribing parking lot attendants so it's sort of unfair to inflict in on him when he's nearly seven.
Panel 10: As he shows off the misshapen result of their collective endeavor, John calls it a design built by a committee. It should be noted that Elly finally showed up so that she could stifle a belly laugh.
Summary: The message conveyed in this strip and strips like it is, of course, "keep your children at arms' length because they're going to mess up what you're trying to do"; after all, Lynn has to justify Elly shooing them away from her, John forting up in his workshop, Mike barricading himself in the den to ticki-tacka-tappa away and, if the strip had continued, Liz locking herself in her room so she can pretend to grade papers while avoiding James Allen and that weird Frenchy girl.
ETA: In the banner, Lynn uses a throw-away panel from one of those depressing strips I linked to.