Working with children can be rewarding but also highly demanding. You will also usually need a specific set of qualifications and experience to show you are up to the job. It is best if you are able to get some work experience first, so you can hit the ground running.
You could volunteer in a school in order to get some direct experience with children. Teachers will probably ask you to help out with lessons and classroom work, checking that children are behaving and completing their work as they should.
You might also want to do something where you can earn some money. In this case, childminding or working in childcare could be a good option. You may get into it quicker if you have some qualifications, however, if you are willing to start at a junior level you might be able to get a job in a nursery school or childminding centre.