Here is a list of useful websites to help you look for a babysitter. Please be careful when choosing someone to care for your child: always ask for and check references, and have a telephone interview before inviting someone to your home.
There is a childcare section in this one but you will have to sift through to find ones relevant to the Netherlands
There are lots of people here offering nanny, au pair and babysitting services. All in English ! Be sure to check both domestic services as well as playgroups and daycare listings.
Oppas Markt is for finding a childminder. This is usually someone who looks after your child in their own home.
Oppasser Gezocht is for finding a babysitter. Fill in your town in the first box to find babysitters in your area. You will have to pay €7.95 to get access to contact information for 3 months.
Go to Diensten -> Oppas en Kinderopvang. Type in your postal code in the box next to the "ZOEK" button (top right). Click the tab "aangeboden" (3 lines down). In the "alle afstanden" menu choose the radius from your house of <5km or <10km and push "Zoek" (find).
Speurders has advertisements which are mostly in Dutch, for babysitters, childminders, nannies and au pairs. Visit Speurders, go to "Kind en Baby" and then "Oppas gevraagd en aangeboden". Choose which location in the left margin.
Via Via has advertisements which are mostly in Dutch, for babysitters, childminders, nannies and au pairs. Visit Via Via, go to "Personeel & Dienstverlening" and then "Oppas". In the right hand margin choose 'aangeboden' and select the province you're located in.
You a set fee for 8 weeks of access to the site. There are lots of babysitters on here, and you can search by area, age, whether references are present etc etc. Unfortunately it´s only in Dutch but well worth asking someone to help you with if you can't read Dutch yourself.