First instinct would be to pay off mortgage, buy a Porsche and book a luxury ski holiday…
After pondering it for a while I’d be thinking how I could make an ongoing, positive change to the quality of life for me and the family, in which case it might be more along the lines of working a shorter week. I’d also take a long hard look at my retirement planning.
That said, when the kids are bigger/older this house is going to feel small and noisy, so maybe a house move would be on the cards…?
In truth, I don’t know the answer to the OP’s question 😆