The Family Circus children have no consistency. In one comic they’re asking why they can’t eat the candy bars out of grandma’s Diaper Genie, and in the next they’re making puns about 50’s art movements.
The age never mattered. There's a tradition in cartooning of ignoring the age of a child when considering his/her demeanor and degree of sophistication. See: Calvin and Hobbes. Cartoon kids will act according to their age when it feels relevant. Other times, they won't.
— Andrew Hussie on why he chose to make the kids in Homestuck thirteen
(Dexter is worried about an electrician that's come to the house)
Dexter: This could be more serious than I thought! This could be a spy from the government! Or worse! This requires me to consult with my adviser.
(cut to Dexter running into the kitchen)
Dexter: Mommy! Mommy! Mommy! There is a big, hairy stranger in the garage! And he's messing with all sorts of stuff!
—Dexter's Laboratory, "Repairanoid"
