Only the vaccination against poliomyelitis is legally obligatory in Belgium. After your child has received the last dose (at 15 months), you will receive a certificate, which you will need to submit to the commune before your child reaches 18 months. Other vaccinations are normally received and administered by the health authorities of the country.
These are the vaccins that children usually get in Belgium: http://www.vaccination-info.be/assets/files/Doc_ONE/rdv_vaccins_2016.pdf