Local history and heritage usually comes with a roof.
Even if it's pouring outside, there are places to explore that will keep you dry, or let you dry off. Old or interesting town centres, museums, galleries, arts centres and historic homes - all offer partial or complete protection from the elements.
There may be any number of more child-friendly local attractions. Is there a prehistoric cavern nearby, an aquarium or a local farm with an animal petting zone? History is being more effectively brought to life all the time; perhaps there's a historic centre near you that will take you and your family back to the past, just for the afternoon.
If you have effective waterproofs, the rain need not be a problem, especially where children are concerned. As long as you're away from busy roads, walking in the rain can be fun. Or make a virtue of the weather by getting even wetter. Explore local parks and forests, take water pistols and other squirters, divide into teams and draw the family battle lines...
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