It's a reminder of how spineless Elly really is; this time it's Mike who points this out.
Panel 1: We see a bleary-eyed, frowning Elly carrying Lizzie and holding Michael's hand; Mike says "Mom? Mom? Can we have a toy? Please?" while Lizzie says "WANT TOY!!"
Panel 2: As they walk down the mall corridor, Lizzie says "Want toy! Want one!" while Mike asks "PLEASE, Ma? Just one, huh? Please MOM?"
Panel 3: After Elly bellows "WE'LL SEE!!!!", Lizzie starts back in with "Want toy, want...."
Panel 4: Her wailing is cut off by Mike who says "That's enough, dummy; she just said yes." We don't see Elly's face but given that her shoulders are up, she's probably frowning the Squished-Up Frown of Rage.
Summary: What we're meant to think is that children are manipulative little finks who only pretend to feel upset to ruin Mother's day and trick her into buying things; what this actually teaches us is that Elly hasn't got what we might call a spine. Instead of being able to resist the temptation to cave in to hucksterism, she gives in so she can be more put-upon.
