Yes sure, first idea that comes to mind when the clouds are dark grey and the rain falls horizontal from the sky is the famous Monkey Town. But if you have no noise-cancelling headphones we might find you some other great kid`s activities for those days in Haarlem.
Library A place that always works out. The kid's section provides low shelves and cabinets, small chairs, books for every age of course. Talking, reading and playing peacefully is absolutely tolerated, even welcome. Check the agenda for kid´s activities like reading hours in different locations. Kids can get a library membership for free! https://www.bibliotheekzuidkennemerland.nl/
Rataplan Explore the world of forgotten things! The Rataplan is a social store where you can drop off clothes, toys and furniture. But you can also dive into the shelves, marvel at retro clothes, beloved toys and just explore the huge world of abandoned things. My kids love the Rataplan! https://rataplan.nl/
Greenhouse Kweektuin A hidden gem, an exotic place to relax a bit is the greenhouse in the Kweektuin. The second you open the door you will be embraced by jungle feeling, tropical climate and invigorating light. Kids can watch the turtles, explore the huge plants or have a tiny picnic at one of the small tables. https://www.haarlemmerkweektuin.nl/plattegrond/
Puddle-jumping In the Netherlands there is a saying that “we are not made of sugar” when it comes to a walk in the rain. Or as my grandma used to say “rain is good for your hair” - you already get it: an outdoor activity IN THE rain is a reasonable option. Some puddle-jumping with a hot shower afterwards or a walk in the forest. It's doable and actually more fun than you think. Grab your raincoat and go!
Public transport We might hate public transport with all our heart as it reminds us of work trips, crowded trains and delayed arrivals. But kids do love a decent bus trip! Pick a time outside rush hour, maybe a scenic tour along the coast (the bus line to Zandvoort maybe) and step in. You will be surprised how relaxing a loop through the city can be:).