In Brussels, see the STIB website for ticket and reduction prices: http://www.stib-mivb.be/article.html?_guid=003e3783-1d83-3410-eab3-ce6aa344e8e2&l=en
TEC https://www.infotec.be/en-us/buyingaticket/ticketsandfares.aspx
De Lijn https://www.delijn.be/en/vervoerbewijzen/abonnementen/buzzy-pazz.html