Unicef estimates that more than 200 million children are living on the streets globally.
By Catherine Lyst
BBC Scotland news website
In Uganda, the problem is exacerbated by the fact that rebel groups are snatching homeless youngsters and forcing them to become child soldiers.
Marsali Campbell, a nurse from Portree in the Isle of Skye, has been working for a mission in Kampala, the country's capital, where she helps to turn around the lives of these vulnerable children.
The 38-year-old, who has worked as a nurse for 20 years, spent time at Great Ormond Street Hospital in London and has a diploma in child health, specialising in children with cancer and HIV.
She first went to Uganda in 2001, having already spent a year working with poor children in India.
A missionary with the African Inland Mission, she has most recently been working with Dwelling Places, which helps street children, abandoned babies and high risk slum families.
Many of them have HIV or have lost parents to Aids.
"The heart of what we do is to try to rescue children from the street," Marsali said.
"Many suffer from depravity, disease, hunger and abuse. We see newborns to teenagers and families headed by children."
Marsali has witnessed five-year-olds living alone on the street and has even seen teenage girls who have spent their whole life on the streets having their own babies while homeless.
These are broken, troubled children who have only ever known suffering
She has also come across numerous abandoned babies. They have been found on the street, in dustbins, tied up in plastic bags and found in pit latrines and swamps.
A particular threat in Uganda is the Lord's Resistance Army (LRA), a rebel group which has committed numerous abuses and atrocities, including the abduction, rape, maiming, and killing of civilians, including children.
Many of the children are trained as guerrillas. The LRA has also abducted young girls as sex and labour slaves.
Other children, mainly girls, have been reported to have been sold, traded, or given as gifts by the LRA to arms dealers in Sudan.
In addition to being beaten, raped, and forced to march until exhausted, abducted children are forced to participate in the killing of other children who attempt to escape.
Amnesty International reported that without child abductions, the LRA would have few combatants.
More than 6,000 children were abducted during 1998, although many of those abducted later escaped or were released.
There are currently estimated to be about 3,000 children still held captive by the LRA.
"We see lots of children who have been abducted by the rebels and escaped," Marsali said. "They often carry a lifetime of guilt.
Many of the children have lived their whole lives on the streets
"We also have children whose whole village has been massacred and they have managed to hide.
"Others are on the streets because of abuse within their own families. They come with wounds, burns and scars.
"These are broken, troubled children who have only ever known suffering."
Apart from using her nursing skills to help the children, Marsali has to build up the youngsters' trust.
"I go and talk to them on the streets about hygiene and sexually transmitted diseases," she said.
Many of the children have HIV or Aids or have lost parents to the virus and have been rejected by their communities.
Latest figures show there are 15 million orphans due to HIV - 12.5 million of those are in Sub Saharan Africa.
"The pandemic of HIV is a major contribution for the number of children ending up on the streets," Marsali said.
Dwelling Places rehabilitates and educates the children they have rescued from the streets.
It's great to see kids grow up that wouldn't have survived otherwise
"A lot of these children have never known a home, having a kitchen, and bathroom, or even just to feel protected," Marsali said.
"Some of them may have HIV but receive no medication while others have the virus unknowingly. Others have seizures or are almost blind and need glasses. Most have never had any dental care."
The youngsters, many of whom have only the rags they were found in, go through a two-year rehabilitation programme.
There are three rehab homes, one for the boys, one for the girls and another for the babies.
Here, the children are encouraged to sleep in a bed, learn to bathe and how to clean their teeth.
"Street children have a reputation for being dirty but they have had no access to soap and have just never been taught the basics," Marsali said.
"They don't know the boundaries of hygiene and violence.
"The word holistic is very important. We need to get to the heart of these kids so they have a future and some hope."
Most children initially go to an interim school where they learn the basics of reading and writing before moving onto a mainstream school.
However, some of the teenage boys who feel they are too old for school receive vocational training.
If it is not possible for them to return to their own communities they go into independent living where a few of them live together.
Marsali welcomes some of the teenagers into her home
Marsali said: "The ones that have done well go back to the streets to talk to the other kids. They're the best advocates."
All the Dwelling Places staff are allocated a group of teenagers who they welcome into their own homes.
"This is so we can really get to know the kids," Marsali said. "At my place they can just be like normal teenagers, listening to music and watching movies.
"I also have teenage girls around with their babies. This allows them to bath their babies and bond with them. And its just good for them to hear they're doing a great job."
Some of the situations Marsali finds herself in can be dangerous but she finds that she is often given protection from the children themselves.
"They will tell others who I am so not to steal from me and they'll protect my car when I'm out," she said.
"Some of them are high on drugs and can seem aggressive but they are never aggressive towards me."
She has also worked in volatile areas such as Karamoja in the north east of the country where there are a lot of problems with drought and cattle rustling warriors who kill many of the men.
"There are a lot of guns out there and you never lose the sense of danger," Marsali said.
She said the most rewarding part of her work is seeing the children change.
'Proud and happy'
"Just to see them putting on shoes for the first time, sleeping in a bed, going to school and having the freedom to play," she said.
"They are proud and happy and just shine.
"It's also great to see kids grow up that wouldn't have survived otherwise.
"To see an abandoned baby grow up and become adopted, turning into a happy, healthy child or to see a child dying from HIV on drug therapy and doing well at school.
"Or just to see a teenager opening up after being full of anger and frustration. To see them learn to trust again and have relationships.
"Or to tell a girl who has been raped or abused with no self esteem that she is important and beautiful. To be able to hug them with normal love. That is amazing."
Marsali is currently giving a number of talks to churches and community groups in Scotland about her work and is hoping to help get Dwelling Places registered as a charity in the UK.
After six years in Uganda, she will be returning to the country next year and plans to open a mobile clinic, providing free health care.
She also hopes her work will be expanded into more remote areas and into other African countries such as the Congo and Central African Republic.
"We need to give these kids a safe place," she said. "We owe it to them."