Up to age 18, you are always entitled to child benefit. When you exceed this age and continue your studies, you depend on the hours you are allowed to work in your region. In Flanders and Wallonia, you may not work more than 650 hours per year to still be entitled to child benefit.
Do you live in Brussels? You can work up to 240 hours per quarter to keep your Groeipakket, regardless of whether you have used the 650 hours or not. Only in July, August, and September can you work unlimited hours if you continue studying after the summer.