You have probably gained some experience in childcare in your home country already. However, every child is different and children in different age groups need a different approach. Your host family will explain to you in detail how to handle their children (what is allowed and what is forbidden, what kind of games they like to play, how you should react if the children do something that is not allowed etc.) and they will inform you about their daily routine (what time they get up, when they go to school, etc.).
Before travelling to The Netherlands, we advise you to do some more reading about the development and needs of children and how to take care of them.