Proposed legislation would allow the euthanasia of minors so long as they are judged capable of deciding for themselves -- a move favoured by three quarters of Belgians, according to a recent opinion poll.
One Wednesday, 16 paediatricians called on lawmakers to vote for a practice some experts say already happens outside the law.
"Why deprive minors of this last possibility," they said in an open letter carried in the press, arguing that under-18s were able to make an informed and mature decision when facing death.
"Experience shows us that in cases of serious illness and imminent death, minors develop very quickly a great maturity, to the point where they are often better able to reflect and express themselves on life than healthy people."
However, a group of religious leaders who oppose the legal change published a statement Wednesday calling for their voice to be heard in a debate "which concerns our whole society."
"We express our deep concern at the risk that such a grave subject will be increasingly trivialised," said the group of Christian, Muslim and Jewish leaders.
"The euthanasia of fragile people, be they children or incapable, is totally inconsistent with their condition as human beings."
"We cannot accept a logic which will lead to the destruction of society's foundations," they said.
A 2002 law made Belgium the second country in the world after The Netherlands to legalise mercy killings for those suffering from incurable illnesses.
Unlike Belgium, however, the Dutch law allows euthanasia for children over 12.
In 2009, Luxembourg also approved euthanasia, for adults only, after parliament pushed through a change to the constitution to get around opposition from the Grand Duke.
In Switzerland, doctors can assist a patient seeking to die but euthanasia itself is illegal.
The issue is hugely controversial and raises a host of ethical problems but a majority of Belgian lawmakers is thought to favour the change.
However, jockeying within the coalition government means a vote is unlikely for some time and may not happen before elections in May 2014.
Belgium logged a record 1,432 cases of euthanasia in 2012, up 25 percent.
There are strict conditions for euthanasia including that patients must be capable, conscious and have to present a "voluntary, considered and repeated" request to die.