In Belgian schools, public education is mainly taught in French, Dutch or German (the 3 official languages). There are private international schools offering education in other European languages (English, German etc) such as the European Schools but their fees are quite high. Please check with your commune to know which schools are available and their languages. Some schools offer languages courses such as Russian, Arabic etc during wednesday and weekends.
There are language schools for children that offer a variety of different languages, but these often only start at the age of 3 and have to be paid. Please check with your commune for more information.
For more information: http://www.centreislamique.be/node/258
http://www.culture-arabe.irisnet.be/Cours%20pour%20enfants.htm