You might need an abacus

In the last month my family has increased by 50% and the number of my sons has increased by 100% - that translates into my family of 4 turning into a family of 6. This means that there are only 2 vacant spaces left in the minivan. And it means there are no vacant spaces left at the dinner table. And it means I have as many children as my parents had. And it means that of my dad's eight grandchildren, half of them are OURS.