How do kids change the FIRE timeline?

Children usually extend the FIRE timeline because they raise your annual expenses — and since your FIRE number is 25x of spending, every recurring child-related cost enlarges the target. Childcare, larger housing, healthcare, food, activities, and possible college support all add up, and higher spending also lowers your savings rate, slowing the climb on both ends. That said, kids don't make FIRE impossible; they make planning more deliberate. Many families fold a specific college figure into the plan (or use a separate 529 so it doesn't inflate the core number), buffer healthcare and life insurance, and accept a later finish date in exchange for the life they want. Some costs are temporary — childcare ends, kids launch — so model expenses in phases rather than assuming today's budget lasts forever. Adjust your projection as the family grows.