In the Netherlands, children start school at the age of 4 (although it is not obligatory before the age of 5). They start school literally the day after their 4 th birthday, if possible, so new children join the class throughout the year. Some of the international schools have a different programme (for instance a nursery group attached to the school). The first decision is therefore whether to have Dutch or English-speaking childcare and/or schooling. The options for the former are naturally much more varied, and it is of course a great step towards getting really involved in Leiden. Many of the leaders (leidsters) can speak some English or French and can help if your child is getting stuck.
If you require full childcare, the options are crèche, oppasmoeder (childminder) or a 'nanny' at home. If you just want your child to spend some time with other children in a pre-school environment, there are pre-schools (peuterspeelzaalen) for children aged 2-4. These are usually a few hours a few mornings (or afternoons) a week.
In the Netherlands, if both parents are working (and freelance work counts) then you are eligible for a contribution towards your childcare: depending on how much you earn, this can be very substantial. There is one specifically English-speaking company that can help you sort this out (it is very complicated) www.blueumbrella.nl they are nice and very efficient