No, in Belgium your children cannot renounce their inheritance prior to your death because that would be entering into an “agreement as to the succession”, i.e. a written contract in which a person, who is not yet deceased, would agree in advance with his/her heirs how his/her assets will be distributed after his/her death. In Belgium, it is currently prohibited to enter into such agreements. This is called the prohibition of entering into an “agreement on future successions”, i.e.  an agreement as to the succession of a person who is still alive.

There are a number of exceptions to this principle in Belgium, in particular the so-called “Valkeniers pact”, which applies to couples having children from a prior relationship. They can enter into an agreement with one another in order to limit the statutory share reserved for the other spouse, so as to ensure that their children from a prior relationship are not disadvantaged. They can do so either by marriage contract or by an act of amendment to the matrimonial property regime.