Actually thy knew exactly what they were doing and the two houses of congress was a compromise to get both the small and large states on-board to accept the constitution. The small states wanted every state to have equal representation, the large states argued that equal representation would give the small states an excessive amount of power at the expense of the large states. They favored representation based on population, but the small states argued that they would then be dominated by the most populous states. The compromise was two houses of congress, The Senate based on equal representation and the House based on population.
However, my assiduous perusal of the Federalist Papers and Ben Franklin's billets doux to Martha Washington have convinced me beyond any shadow of historical doubt, that those gentlemen were not thinking of ragtag and bobtail outfits like Delaware and Rhode Island.
Hell, they couldn't think of everything. They even ignored Maine and Vermont!