In Belgium, infants can go to school as from the age of 2.5 years. They first spend 3 years in a nursery school, to prepare for primary education which starts at the age of 6. From that moment, it's obligatory to have your children go to a school. Between 3 and 6 years of age, Flanders has a so-called "compulsory education" system. The children don't necessarily have to go to school, but they have to receive some kind of education.
Only a small minority of the children, some 3,000, is not going to a public school from the age of 3. In this group, 1 in 3 children are going to a private school, to a school abroad or they are receiving private education at home. The other 2,000 children are probably not going to school at all and may not be receiving any kind of education to prepare them for primary school.