A rainy-day backup is only useful if you can actually reach it when the weather changes. A museum on the other side of the city may be appealing, but it can turn a short adjustment into another long journey with wet bags and tired children.
Before the outing, choose an alternative near the place you expect to be. Check its opening hours, entry arrangements and suitability for the ages in your group. Do not assume that an indoor attraction can accept everyone immediately without a reservation.
Match the size of the change
Light showers may call for a shorter walk and a longer meal rather than a completely different destination. Steady rain or unsuitable conditions may justify changing the whole plan before leaving home. Read the forecast's timing and relevant local notices, not just the weather symbol beside the day.
Keep the backup within a budget you are comfortable using. An unexpected expensive attraction can create another decision at the least convenient moment. A library visit, a suitable indoor public space or returning home for an activity may be a better alternative where available.
Pack for the transition
Bring weather-appropriate layers and a way to contain wet belongings. Consider where bags and coats can go at the alternative venue. A large collection of damp items can make a small indoor space difficult to use even when the destination itself is appropriate.
If there is a fixed booking in the original plan, read its cancellation or weather policy before assuming you can move it. Keep the provider's current contact information accessible for changes that require their help.
Explain the new plan clearly
Tell children what is changing and what will still happen. Avoid promising a replacement that you have not checked. It is reasonable to acknowledge disappointment without trying to make the alternative sound better in every way.
Let the adjusted day be smaller if that is what works. A comfortable meal and a short indoor visit can be enough after a difficult start. The backup does not have to reproduce every planned hour.
When you return, note whether the alternative was genuinely convenient. That information will improve the next plan more than adding another distant attraction to a long list of possibilities.