Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic shows a conversation between a couple discussing family planning. One partner says "I really think we should have two kids," and the other emphatically responds "No! Not five!" -- apparently mishearing or exaggerating the number. The first partner asks "Can you imagine us with five kids?" and the other says "No, of course not."

The final panel shows a thought bubble where the person imagines themselves with five children climbing all over them in a chaotic scene. The joke is that despite claiming they can't imagine having five kids, the character immediately and vividly imagines exactly that -- and the mental image is clearly overwhelming and nightmarish. The comic plays on the gap between what we say we "can't imagine" and our brain's insistence on imagining it anyway, as well as the universal parental anxiety about being outnumbered by children.