Classes and sports are a great way to get your children in contact with other children, get them moving, or help them develop skills. They also offer you the chance to meet other parents. Most of the classes etc for children below are in Dutch, but it is usually easy to follow and if necessary teachers are almost always prepared to try at least to explain it in English if need be. It is a great help to your Dutch to immerse yourself in a bit of language!
Costs: The costs vary, but do be aware that if your income is low (approximately under 1400 net per month for a couple and 1300 net per month for a single parent) you may be eligible for state support to enable you and/or your child to do a course or activity. You will need to fill out a form, keep your receipts and you should be able to receive up to € 200 per year back.
There is also a system whereby children aged 5+ can try out various different sports to see which they like, at different state-subsidized sport schools etc. Your child should receive a list at the beginning of Group 3 if they go to a Dutch school.
There are also lots of activities going on in the neighbourhood centres (buurthuizen) dotted around the city. To find out what's on at your nearest buurthuis go to www.libertasleiden.nl , click on 'informatie', click on 'buurtcentra' (in red), then click on the one nearest you, and then click on 'kinderen' for children's activities and 'activiteitenrooster' for a roster of all activities. For instance, Buurthuis de Pancrat on Middelstegracht (near Albertheijn in the city centre) has homework club on a Wednesday afternoon, craft club on a Thursday afternoon (ages 4-12), and a cooking workshop once a month (ages 9-12). These activities are all in Dutch of course, but are a great way to meet people in your area from all backgrounds. There are also frequently parties and special events: these will usually be advertised on What's on This Week but if you know of something that isn't, please let me know!
There are literally hundreds of classes, sports and activities going on in Leiden, and this list is certainly not exhaustive. If you have one you would like to add please do let me know!