By Greg Barrow BBC correspondent at the United Nations

The UN Special Session on Children, which begins on Wednesday and runs until Friday, will look at issues affecting children around the world.

The meeting, at the UN headquarters in New York, has attracted more than 60 heads of state - most from the developing world, representing countries where children and young people make up more than half the populations.

Children will also be participating at the highest levels for the first time - not exactly a radical concept considering the subject matter of the Special Session, but it is something that has not happened in the past.

Groups campaigning for children say increasing the participation of young people is a way of making sure that their views, concerns and aspirations are taken into account by the adults who generally have the final decision on setting out targets for the future.

Document deadline

The agenda of the Special Session reflects the whole spectrum of issues that affect children around the world.

There is no particular focus, and delegates will end up discussing everything from child poverty to education, sexual abuse, the role of children in conflict zones, and much more.

Children are often caught up in conflicts

Most of these issues are addressed in what is being called the "outcome document", which delegates hope to adopt by the end of the Special Session on Friday.

The document is designed to set new targets for the international community in, among other areas, reducing child mortality, increasing access to education, and improving access to health services.

'Unholy alliance'

The document has already been the subject of lengthy negotiations, and much of it has been discussed and finalised in advance.

There are, however, a number of extremely contentious areas of the document touching on issues such as children's rights, and their access to health services, that include abortion.

What some campaigners are calling "an unholy alliance" of the United States, Muslim nations, and countries where there is a strong Catholic following, has been campaigning for the removal of any reference in the document to "health services", as this is assumed to be a code for abortion.

The US views any attempt to give children more rights as a threat to the nuclear family

This group of countries also wants a lower priority to be given to areas of the document focussing on reproductive and sexual health - conservative groups in this camp argue that abstinence is the best recipe for avoiding unwanted pregnancies and sexual diseases among children, and this should promoted above sex education for children.

Another controversial area, as far as the United States is concerned, is the whole issue of children's rights.

Whose rights?

The US is one of only two countries in the world, the other being Somalia, that have not ratified the UN convention on the rights of the child.

The US believes its own national laws protecting children are more than adequate, and views the UN convention, or indeed any attempt to give children more rights, as a potential threat to the role of parents, and the whole idea of the nuclear family.

The wording of passages on health is contentious

US negotiatiors have worked hard to have any reference to children's rights withdrawn from the outcome document.

It is a stance that has drawn fierce criticism from groups campaigning on behalf of children.

They view it as a callous attempt to undermine one of the pillars of the global framework designed to protect and improve the lives of children.

Delegates fear that arguments over these issues may distract attention away from a gathering that was initially conceived to set new international standards for the world when it comes to the treatment of children.

Most are expecting negotiations over the wording of the outcome document to drag on to the very end of the Special Session, and they're not ruling out the possibility that agreement will not be reached by Friday evening.