Save for a family cost, but keep cash for a bad day. Use separate savings pots:...

https://www.toddleabout.co.uk/parenting/planning-for-big-family-costs-without-losing-your-financial-buffer/

Save for a family cost, but keep cash for a bad day. Use separate savings pots: one for your goal, one for bills. Add a sum each month. Test it with an awkward month: less pay or a car fix