The legislation appears to have wide support in the largely liberal country. But it has also aroused intense opposition from foes - including a list of paediatricians - and people who have staged noisy street protests, fearing that vulnerable children will be talked into making a final, irreversible choice.
Backers like Dr Gerland van Berlaer, a prominent Brussels paediatrician, believe it is the merciful thing to do. The law will be specific enough that it will only apply to the handful of teenage boys and girls who are in advanced stages of cancer or other terminal illnesses and suffering unbearable pain, he said.
Under current law, they must let nature take its course - or wait until they turn 18 and can ask for euthanasia.
"We are talking about children that are really at the end of their life. It's not that they have months or years to go. Their life will end anyway," said Dr Van Berlaer, chief of clinic in the paediatric critical care unit of University Hospital Brussels. "The question they ask us is: 'Don't make me go in a terrible, horrifying way, let me go now while I am still a human being and while I still have my dignity.'"
The Belgian Senate voted 50-17 last December 12 to amend the country's 2002 law on euthanasia so that it would apply to minors, but only under certain additional conditions. Those include parental consent and a requirement that any minor desiring euthanasia demonstrate a "capacity for discernment" to a psychiatrist and psychologist.
The House of Representatives, the other chamber of Parliament, is scheduled to debate on Wednesday whether to agree to the changes, and vote on them on Thursday. Passage is widely expected.
King Philippe, Belgium's constitutional head of state, must sign the legislation for it to go into effect. So far, the 53-year-old monarch and father of four has not taken a public position, but spokesman Pierre De Bauw said that is not unusual. "We never give any comment on any piece of legislation being discussed in Parliament," Mr De Bauw said.
Though one opinion poll found 75% of Belgians in favour, there has been a vocal opposition.
"We are opening a door that nobody will be able to close," said Andre Leonard, the archbishop of Mechelen-Brussels and chairman of the Episcopal Conference of Belgium, told The Associated Press. "There is a risk of very serious consequences in the long term for society and the meaning we give to life, death and the freedom of human beings."
This week, an "open letter" carrying the names of 160 Belgian paediatricians was issued to argue against the new law, claiming there is no urgent need for it and that modern medicine is capable of soothing the pain of even the sickest children.
The doctors also said there was no objective way of providing that children possess the "discernment" to know what euthanasia means.
Besides Belgium, the only other countries to have legalised euthanasia are the Netherlands and Luxembourg, said Kenneth Chambaere, a sociologist and member of the End-of-Life Care research group at the Free University Brussels and University of Ghent.
In Luxembourg, a patient must be 18. In the Netherlands, children between 12 and 15 may be euthanised with parents' permission, while those who are 16 or 17 must notify their parents beforehand.